Automotive Computer Controlled Systems.pdf

Automotive Computer Controlled Systems Automotive Computer Controlled Systems Diagnostic tools and techniques Allan W M Bonnick MPhil CEng MIMechE MIRTE OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE N[.]

Common technology

Rapid advancements in electronics technology and manufacturing processes have led to the widespread use of microcontrollers, which serve as the core components of various control systems in modern motor vehicles.

Microcontrollers, like other computers, include a control unit, and to prevent confusion, the term Electronic Control Unit (ECU) has been replaced with Electronic Control Module (ECM) This book consistently uses the term ECM to refer to what was previously known as the ECU.

As vehicle systems evolve, the prevalence of shared electronic and computing technology across various automotive systems highlights the importance for technicians to master this 'common technology.' This knowledge equips them to diagnose and repair a wide range of vehicles effectively Furthermore, many automotive test equipment manufacturers are now offering tools that, when paired with diagnostic trouble code information, empower skilled technicians to confidently maintain and repair modern vehicle systems in the 2000s and beyond.

This article will explore a variety of commonly used modern systems to identify and highlight the key elements worth understanding further.

Engine-related systems

The article surveys commonly used engine systems, specifically ignition, fueling, and emission control The primary aim is to identify shared elements within these systems to concentrate on components that can be effectively tested using affordable tools, rather than focusing on more complex systems that necessitate specialized testing equipment.

Analyzing three ignition systems reveals common elements utilized across various types By exploring additional systems, we can identify fundamental principles shared among different vehicle technologies This highlights the transferable knowledge applicable across a wide range of technological applications.

Ignition systems

THE CONSTANT ENERGY IGNITION

Figure 1.1 illustrates a long-standing electronic ignition distributor, which is powered by the engine camshaft, causing it to rotate at half the speed of the engine.

As each lobe on the rotor (reluctor) passes the pick-up probe, it induces a pulse of electrical energy in the pick-up winding This winding connects to the electronic ignition module, which activates the current to the ignition coil's primary winding once the pulse generator voltage reaches around 1 V.

Fig 1.1 Reluctor and pick-up assembly

As the reluctor rotates, the voltage in the pick-up winding decreases, prompting the ignition module to turn off the ignition coil's primary current, which induces high voltage in the secondary winding for the ignition spark The interval between the ignition coil's primary current being switched on and off is termed the dwell period As engine speed increases, the dwell angle effectively increases, allowing the coil current to reach its optimal value across all speeds The pulse generator voltage varies with the rotation of the reluctor, with ignition coil primary current activating at around 1 V and deactivating when the voltage returns to this level At higher speeds, the pulse generator generates a higher voltage, resulting in an earlier activation of the ignition coil, while the deactivation point remains unchanged, leading to an increased dwell angle as speed rises This ensures that the build-up time for the coil's primary current, crucial for spark energy, stays nearly constant at all speeds, which is why these ignition systems are referred to as 'constant energy systems.' Additionally, this type of electronic ignition still utilizes centrifugal and vacuum mechanisms for automatic ignition timing adjustments.

DIGITAL (PROGRAMMED) IGNITION

Programmed ignition utilizes computer technology to eliminate the need for traditional mechanical and pneumatic components found in conventional distributors This advancement is exemplified in early digital ignition systems, as illustrated in Figure 1.3.

Fig 1.2 Pick-up output voltage at low and high speeds

The Engine Control Unit (ECU), also known as the Engine Control Module (ECM), is a compact computer that interprets input signals from the engine, including speed, crank position, and load By comparing these readings with pre-stored data, the ECU regulates the ignition system's outputs Typically, engine test data is visually represented as a three-dimensional map for analysis.

Fig 1.4 An ignition map that is stored in the ROM of the ECM

Any point on this map can be represented by a number reference: e.g engine speed, 1000 rpm; manifold pressure (engine load), 0.5 bar; ignition advance angle,

Digital ignition involves converting numerical values into binary code, consisting of 0s and 1s This data is stored in the computer's memory, enabling the control unit's processor to determine the appropriate ignition settings for various engine operating conditions.

In this early type of digital electronic ignition system the ‘triggering’ signal is produced by a Hall effect sensor of the type shown in Fig 1.5.

The Hall sensor operates by producing a voltage pulse when the gaps in the rotating vane expose it to the magnetic field, resulting in a zero output when the metal part is positioned between the magnet and the Hall element This mechanism is crucial for generating a spark in electronic ignition systems While traditional ignition distributors are still in use, modern systems often rely on a crankshaft and flywheel-driven trigger pulse generator, which eliminates the need for a conventional distributor This highlights the evolution of ignition systems towards more efficient designs that utilize flywheel-driven pulse generators.

DISTRIBUTORLESS IGNITION SYSTEM

The ignition system for a four-cylinder engine, as illustrated in Figure 1.6, features two ignition coils—one serving cylinders 1 and 4, and the other for cylinders 2 and 3 A spark is generated when a pair of cylinders approaches the firing point near top dead center (TDC), resulting in sparks during both the exhaust and power strokes Consequently, this ignition system is often referred to as the 'lost spark' system.

Figure 1.6 illustrates two sensors located at the flywheel: one sensor measures engine speed while the other serves as the ignition trigger These sensors, detailed in Fig 1.7, operate based on the variable reluctance principle.

An alternative method for identifying the Top Dead Center (TDC) position involves a toothed ring attached to the flywheel, featuring a missing tooth at the TDC location This setup functions as a variable reluctance sensor, where the absence of an electrical pulse indicates the TDC position Additionally, the remaining teeth on the reluctor ring, typically spaced at 10-degree intervals, generate pulses for monitoring engine speed.

Fig 1.7 Details of engine speed and crank position sensors

Fig 1.8 Engine speed and position sensor that uses a detachable reluctor ring

OPTOELECTRONIC SENSING FOR THE

The electronic ignition system in Kia vehicles features a photoelectronic distributor sensor, as illustrated in Figure 1.9 This system operates using two key electronic components: a light-emitting diode (LED) that transforms electrical energy into light, and a photodiode that activates when illuminated by the LED.

The rotor plate in this sensor design features 360 slits spaced at 1° intervals for accurate engine speed detection, along with several larger holes positioned closer to the center for Top Dead Center (TDC) indication Among these larger openings, one is notably wider than the rest, specifically serving to mark the TDC for the number 1 cylinder.

With the rise in microprocessor processing power, system designers are leveraging this enhanced capability to integrate advanced features like combustion knock sensing and adaptive ignition control.

Fig 1.10 An alternative form of optoelectronic sensor

KNOCK SENSING

Combustion knock is a common issue in engine operation, historically managed by a hand control that allowed drivers to retard ignition upon hearing the distinctive 'pinking' sound Once the knock subsided, drivers could revert the control to its advanced position Modern vehicles utilize electronic controls to automate this process, often incorporating a knock sensor within the electronic ignition system Figure 1.11 illustrates a knock sensor installed on the cylinder block of an in-line engine.

The piezoelectric effect is utilized in knock sensors, allowing for the detection of combustion knock by filtering out other mechanical noises through the tuning of the piezoelectric element and sensor circuit design When combustion knock occurs, it generates a voltage signal sent to the Engine Control Module (ECM), which responds by gradually retarding the ignition to prevent further knocking The ECM adjusts the ignition timing in increments of approximately 2 degrees until knocking stops, after which it advances the ignition in small steps until the optimal setting is achieved.

Figure 1.11 shows the knock sensor in position The operating principles and test procedure are described in more detail in Chapters 5 and 7.

ADAPTIVE IGNITION

Modern Engine Control Modules (ECMs) leverage advanced computing power to optimize ignition systems by adjusting settings in response to the wear of components like petrol injectors The key principle is to achieve optimal engine torque, which occurs when combustion generates maximum cylinder pressure just after Top Dead Center (TDC) The ECM utilizes a crank sensor to monitor engine acceleration and evaluate the impact of ignition adjustments on performance, indicated by increased engine speed as specific cylinders fire If improvements are noted, the ignition memory map can be updated accordingly.

The knock sensor on the engine plays a crucial role in the adaptive learning strategy utilized by the ECM, which adjusts settings based on real-time data This strategy is prevalent in computer-controlled systems, requiring technicians to operate vehicles under normal conditions for several minutes after replacing parts or making adjustments A review of ignition systems reveals common technological features, including crank position and speed sensors, ignition coils, knock sensors, and manifold pressure sensors that indicate engine load The subsequent section will explore computer-controlled fueling systems, highlighting their technological similarities to electronic ignition systems.

Computer controlled petrol fuelling systems

SINGLE-POINT INJECTION

Petrol injection involves a single injector that sprays petrol into the induction manifold near the throttle butterfly valve, enhancing engine performance and efficiency.

Finely atomized fuel is injected into the throttle body based on signals from the engine computer (EEC, ECM), ensuring an optimal air-fuel ratio for various conditions This system employs the speed density method to measure the mass of incoming air, as opposed to using an air flow meter found in other systems The computer calculates the necessary fuel amount for specific conditions to maintain efficient engine performance.

The single-point injection system is crucial for accurately measuring the air entering the engine By utilizing the speed density method, this system gathers essential data from the manifold absolute pressure (MAP) sensor, the air charge temperature sensor, and the engine speed sensor to optimize engine performance.

Fig 1.14 The single point CFI (central fuel injection) unit

Computer controlled petrol fuelling systems 13

The central injector unit, depicted in Fig 1.14, operates through a solenoid (3) that receives electric signals from the engine control computer During full or partial engine load, the injector sprays fuel with each induction stroke, while at idle, it injects fuel once per crankshaft revolution The fuel pressure regulator ensures a consistent fuel pressure at the injector valve, with the injected fuel quantity being controlled by the duration the solenoid keeps the valve open.

The throttle plate (butterfly valve) motor is operational during starting, coasting,when shutting down the engine, and when the engine is idling.

MULTI-POINT INJECTION

In petrol injection systems, injectors receive pressurized petrol via a fuel gallery or 'rail', with each injector linked to the gallery through individual pipes.

The fuel pressure in the gallery is regulated by a specialized device, ensuring a maximum pressure of 2.5 bar, as depicted in Fig 1.16 This pressure regulator is calibrated during the manufacturing process to maintain optimal fuel performance.

The petrol pump operates by delivering more fuel than necessary for injection, causing excess pressure to lift the regulator valve off its seat This mechanism allows the surplus fuel to return to the fuel tank through the return connection.

The internal diaphragm of the fuel pressure regulator is influenced by inlet manifold pressure, allowing it to adjust fuel pressure for various operating conditions When the diaphragm is raised against the spring, it reduces fuel pressure to about 1.8 bar Conversely, when the diaphragm is lowered due to increased pressure in the inlet manifold from a wider throttle opening, the fuel pressure increases to approximately 2.5 bar.

The fuel injection system regulates the amount of fuel sprayed into the inlet manifold by controlling the duration the injector valve remains open By adjusting this time, the system can tailor the fuel injection to meet varying performance needs.

Engine fuelling requirements are programmed into the ECM's memory by the designer During operation, the ECM collects data from various sensors related to the engine's fuel needs It compares this real-time data with the pre-stored information in its memory Based on this comparison, the ECM generates output signals that are sent as electrical pulses to the injector cables, with the duration of these pulses varying within a specific timeframe.

2 milliseconds (ms), to around 10 ms The ‘duty cycle’ concept is based on the

Computer controlled petrol fuelling systems 15

A typical square waveform is shown in the figure, a single cycle is indicated by 'C', which consists of an ON time 'A', and an OFF time 'B'.

Duty cycle is the length of the ON time 'A' compared to the whole cycle 'C', expressed as a percentage (Please note, On time can be High and Low on certain systems.)

Using the figure and the time periods, the duty cycle is 25 %

Fig 1.17 Duty cycle percentage of the available time for which the device is energized, as shown in Fig 1.17.

The performance and driveability of a vehicle's engine are heavily influenced by the quality of its design inputs, particularly the computer program stored in the read-only memory (ROM) of the Engine Control Module (ECM) A fuelling map, akin to an ignition map, uses throttle position to represent engine load and air/fuel ratio instead of spark advance Each point on this fuelling map is encoded in binary, with a range of these points saved in the ECM's ROM The ECM compares these stored values with input signals from various sensors to accurately determine the duration of the fuel injection pulse.

Franchised dealerships can customize computerized systems to meet customer needs by reprogramming the ROM This process requires qualified personnel and must be conducted under the supervision of the vehicle manufacturer.

Multi-point injection systems commonly use one of two techniques.

1 Injection of half the amount of fuel required to all inlet ports, each time the piston is near top dead center.

2 Sequential injection, whereby injection occurs only on the induction stroke.

The multi-point injection system features a dedicated petrol injector for each engine cylinder, as illustrated in Fig 1.18 Each injector is specifically engineered to spray fuel onto the back of the inlet valve, with variations in injection position and angle depending on the engine type.

The hot-wire mass air flow meter measures air flow in the system illustrated in Fig 1.18 The control computer processes the signal from this meter alongside inputs from additional sensors, including engine speed, coolant temperature, and throttle position, to calculate the duration of the injection pulse.

Sequential multi-point injection refers to a petrol injection system that delivers a separate fuel injection for each cylinder during every operational cycle, enhancing control and efficiency in engine performance.

1 EEC IV module 2 In-tank fuel pump 3 Fuel pump relay 4 Fuel f ilter 5 Idle speed control (ISC) v alv 6 Mass air flo w (MAF) meter 7 Air cleaner 8 Fuel pressure re gulator 9 Fuel rail 10 Throttle position sensor (TPS) 11 Air char ge temperature (A CT) sensor 12 Fuel injector 13 Camshaft identif ication (CID) sensor 14 Carbon canister (EV AP) 15 Pur ge solenoid v alv e (EV AP) 16 DIS coil 17 Battery 18 EDIS-4 module 19 Engine coolant temperature (ECT) sensor 20 HEGO sensor 21 Crankshaft position/speed (CPS) sensor 22 Po wer relay 23 Po wer steering pressure switch (PSPS) 24 A/C compressor clutch 25 Service connector (octane adjust (O (plug-in bridge during production for operation with Premium R unleaded fuel 26 Self-test connector 27 Diagnosis connector for FDS 2000 28 Ignition switch 29 Inertia switch 30 Electronic v acuum re gulator (EVR) 31 EGR v alv e 32 Dif ferential pressure transducer (DPFE sensor) 33 Dif ferential pressure sampling point 34 T o inlet manifold (air chamber) 35 Pulse air f ilter/v alv e housing 36 Pulse air solenoid v alv e 37 A/C radiator f an switching 38 Electronic transmission control (CD4E) Air intak e - atmospheric pressure Fuel supply - lo w pressure Fuel v apour

Air intak e - inlet manifold pressure Exhaust gases ahead of catalytic con v erter Fuel supply - system pressure Exhaust gases after catalytic con v ertor Fig 1.18 A m ulti-point petrol injection system

Engine management systems (EMS) are essential for sequential injection, often utilizing an additional camshaft-driven sensor Hall type and variable reluctance sensors are commonly employed to help the computer identify the top dead center (TDC) of the number 1 cylinder Figure 1.19 illustrates one of these sensors installed in an overhead camshaft engine.

Many sensors utilized in fueling systems, such as crank speed and top dead center sensors, are also employed in ignition systems Additionally, manifold pressure sensors help indicate engine load Due to the dual functionality of these sensor signals for both ignition and fueling, it has become standard practice to integrate them under a single computer system, referred to as an engine management system.

Engine management systems (EMS)

EXHAUST GAS RECIRCULATION

The electronic vacuum regulator and the exhaust gas recirculation (EGR) valve are crucial components in engine management systems, as illustrated in Fig 1.18 To minimize NOx emissions, it is essential to maintain combustion chamber temperatures below approximately 1800 °C, the threshold for NOx formation The EGR system aids in achieving this by recirculating a controlled amount of exhaust gas back into the induction system, effectively lowering combustion temperatures The principle of the EGR system is further depicted in Fig 1.20.

Fig 1.20 Exhaust gas recirculation system

To optimize performance, the EGR system remains inactive during cold engine starts and full-load conditions The accompanying image illustrates the solenoid valve that regulates the EGR valve, which functions based on a duty cycle principle Under typical operating conditions, the EGR system is estimated to reduce NOx emissions by around 30%.

COMPUTER CONTROL OF

Motor fuels give off vapors that contain harmful hydrocarbons, such as benzene.

To minimize hydrocarbon emissions from fuel tanks, vehicles are fitted with a carbon canister that utilizes activated charcoal to capture toxic substances in hydrocarbon molecules This canister is an integral part of the evaporative emission control system, connecting the fuel tank via a valve and pipe.

The evaporative purge solenoid valve plays a crucial role in connecting the carbon canister to the induction system, allowing hydrocarbon vapors to be drawn into the combustion chambers for burning alongside the main fuel-air mixture Controlled by the ECM, the valve operates through duty cycle electrical signals that regulate its opening duration When the engine is off, vapors from the fuel tank are stored in the carbon canister, and upon engine startup, the ECM activates the solenoid valve to facilitate vapor flow into the induction system The valve's operational frequency varies based on different driving conditions.

Evaporative emissions control is part of the emissions control system of the vehicle and it must be maintained in good order.

Anti-lock braking (ABS)

OPERATION OF ABS

The operation of an anti-lock braking system (ABS) involves three critical phases: pressure retention, pressure reduction, and pressure increase When the brake pedal is depressed, the system monitors wheel sensors to prevent wheel lock-up If the front right wheel is about to lock, the computer activates the modulator pump and closes the inlet valve C4, entering the pressure retention phase If the wheel does lock, the system releases pressure by opening the outlet valve D4, allowing for some wheel rotation during the pressure reduction phase Conversely, if the wheel accelerates, the computer will close the outlet valve D4 and open the inlet valve C4 to apply more hydraulic pressure, known as the pressure increase phase These phases continue to cycle until wheel lock is no longer a threat or the brake pedal is released.

SOME GENERAL POINTS ABOUT ABS

The system depicted in Fig 1.23 demonstrates a specific mode of Anti-lock Braking System (ABS) operation, where the front right and rear right brakes maintain pressure, the front left brake experiences pressure increase, and the rear left brake undergoes pressure reduction This functionality is indicated by the positions of the inlet valves C1 – C4 and the outlet valves D1 – D4.

During ABS operation, the brake fluid flows back to the master cylinder, causing noticeable pulsations in the brake pedal that signal the system's activity Once ABS operation ceases, the modulator pump remains active for about one second to ensure the hydraulic accumulators are fully emptied.

Traction control

The differential gear in a vehicle's driving axles allows the inner wheel to rotate more slowly than the outer wheel during a turn, enhancing maneuverability For instance, when a vehicle makes a sharp right turn, the right-hand wheel rotates slowly while the left-hand wheel rotates faster, demonstrating the critical function of the differential gear in maintaining stability and control.

However, this same differential action can lead to loss of traction (wheel spin).

When one driving wheel is on a slippery surface, it may spin while the opposite wheel remains stationary, causing the vehicle to become immobile This loss of traction occurs because the differential gear transmits torque only equal to that of the weakest wheel on the axle, hindering movement.

On a slippery surface, minimal torque is required to initiate wheel rotation, resulting in insufficient torque reaching the non-spinning wheel to propel the vehicle forward.

Fig 1.24 The need for a differential gear

Traction control systems enhance vehicle safety by applying brakes to wheels on slippery surfaces, preventing wheel spin and allowing power transfer to other wheels Once traction is regained, normal driving resumes These systems often feature an electrically operated secondary throttle to reduce engine power and eliminate wheel spin, requiring communication between the engine management and ABS computers via a controller area network (CAN) The ABS system, which includes essential components for automatic brake application, also necessitates additional valves for individual wheel control Some Volvo vehicles illustrate the layout of such traction control systems.

The traction control system, illustrated in Fig 1.26, features an ABS modulator equipped with additional hydraulic valves, solenoid valves, and by-pass valves Focusing on a front-wheel drive vehicle, attention is given to the front right (FR) and front left (FL) brakes When wheel spin is detected at the FR wheel, it necessitates the application of the FR brake to maintain control.

The solenoid valves are closed, effectively blocking the connection between the pump's pressure side and the brake master cylinder, while the inlet valve for the front left brake remains closed to prevent any application of that brake.

Secondary throttle actuator Control from ECM

Fig 1.25 The electrically-operated throttle used with the traction control system

The modulator pump operates continuously during transmission control, drawing fluid from the master cylinder It then channels this fluid through hydraulic valve 1 to the front right (FR) brake via the inlet valve (C4).

When the front right (FR) wheel matches the speed of the front left (FL) wheel, the computer can release the FR brake by operating the valves This brake can then be reapplied until the vehicle operates normally without wheel spin In instances of spin at the FR wheel, control is achieved by opening and closing the inlet valve (C4) and the outlet valve (D4).

When wheel spin is no longer detected and normal driving resumes, the modulator pump deactivates, allowing the solenoid valves to open and the valves (C4) and (D4) to revert to their standard positions for regular brake function The modulator pump supplies more brake fluid than typically needed, and the by-pass valves are engineered to open at a specific pressure, enabling excess brake fluid to flow back into the master cylinder and replenish the brake fluid reservoir.

The system is designed so that traction control is stopped if:

2 there is a risk of brakes overheating;

3 the brakes are applied for any reason;

4 traction control is not selected.

Stability control

Traction control can be enhanced to improve a vehicle's handling, especially during cornering This advanced system is commonly known as 'stability control'.

In Figure 1.27(a), the vehicle experiences understeering, where it attempts to move straight despite the curve ahead To navigate the bend effectively, the driver must increase steering input Stability control aids in this situation by applying brakes to the rear wheel on the inside of the turn, creating a corrective action that helps smoothly realign the vehicle with its intended path.

Oversteer occurs when the rear of a vehicle moves outward, decreasing the turn radius and worsening the condition To counteract oversteer, drivers can apply the brakes on the outside wheels or reduce engine power through the computer-controlled secondary throttle For effective stability control, vehicles must be equipped with additional sensors, including a steering wheel angle sensor and a lateral acceleration sensor, which provide critical information about the levels of understeer or oversteer to the control computer.

To achieve stability control it is necessary for the engine control computer,the ABS computer and the traction control computer to communicate, and

(with stability control) Steered path

Fig 1.27 Stability control; (a) understeer, (b) oversteer

Air conditioning systems utilize the CAN network for communication, as depicted in Fig 1.25 This figure also demonstrates the output format from Hall type wheel sensors For more information on CAN networking, refer to Chapter 2, while details about Hall type sensors can be found in Chapter 5.

Air conditioning

DEALING WITH AIR CONDITIONING

Air conditioning refrigerants can pose health risks to individuals and have detrimental effects on the environment, necessitating specialized equipment and trained technicians for servicing Manufacturers of garage equipment, like the Bosch Tronic R134 kit, offer essential tools for this purpose Additionally, training provided by equipment suppliers and vehicle manufacturers is crucial, as air conditioning systems are now prevalent in many vehicles across Europe It is highly recommended that all garage technicians undergo this training to ensure safe and effective service.

Technicians must adhere to strict regulations regarding the release of refrigerants into the atmosphere and familiarize themselves with local laws It is crucial to repair any small leaks promptly, as refrigerants are stored under pressure Additionally, certain refrigerants can emit toxic gases when exposed to flames, making it essential to prevent such situations Care should also be taken to avoid contact with refrigerants, as they can cause cold burns and eye damage.

These are some of the reasons why special training is so important.

Computer controlled damping rate

Oil is forced through an orifice to create damping in vehicle suspension systems, with the damping force influenced by the orifice size Adjusting the size of the damping orifice, typically via a valve controlled by the ECM, allows for softer or stiffer damping as needed Some Ford systems utilize a solenoid-operated damping valve, managed by an adaptive damping computer, to provide two damping rates: soft and stiff The suspension damping rate is adapted to various driving conditions, including acceleration, braking, bumpy roads, and cornering The computer receives input from multiple sensors, which is compared to design values stored in ROM, enabling the processor to determine the optimal damping rate.

The speed sensor in vehicles is often an electromagnetic type, while the steering position sensor typically employs an opto-electronic design that uses an infrared beam interrupted by a perforated disc Additionally, the wheel speed sensor signal is sourced from the ABS computer, and the brake light signal comes from the stop light switch.

Computer controlled diesel engine

SPILL CONTROL

Figure 1.34 shows a cross-section of a rotary-type fuel injection pump The high pressure pump chamber that produces the several hundred bars of pressure

Fig 1.33 Computer controlled d iesel e ngine

Computer controlled diesel engine management systems 35

The rotary-type fuel injection pump features two outlet ports: one connects to a solenoid-operated spill valve, while the other supplies fuel to the injector When the ECM signals the solenoid to open the spill valve, fuel from the feed pump enters the pressure chamber at 15-20 bar, charging the high-pressure pump element Upon receiving a signal to close the spill valve, the high-pressure pump plungers force fuel through the outlet to activate the injector Once injection is complete, the ECM signals the solenoid to reopen the spill valve, preparing for the next cycle Additionally, the electronic driving unit (EDU) amplifies a 5 V computer pulse to a 150 V supply, enabling high-speed operation of the spill valve.

TIMING CONTROL

The timing control valve is a solenoid-operated hydraulic valve that regulates fuel supply to the plungers, adjusting the rotation of the high-pressure pump cam ring to advance or retard the injection point as necessary Essential sensor inputs for this operation are illustrated in Fig 1.35.

IDLE SPEED CONTROL

The idling speed of a diesel engine is regulated by the fuel injected into its cylinders To maintain a consistent idling speed across varying conditions, the engine control module (ECM) must be programmed to adjust fuel delivery accordingly Sensor inputs, as illustrated in Fig 1.36, play a crucial role in providing the necessary data for this process.

Fig 1.35 Sensor inputs for the timing control valve

Fig 1.36 Diesel engine idle speed control required in order that the ECM can provide the correct signals to the spill control valve.

The common rail system represents a significant advancement in computer-controlled diesel systems, where fuel is kept at a constant high pressure within a common rail Each injector features a solenoid-operated control valve, managed by the Engine Control Module (ECM), which dictates the timing of injection based on a ROM program and sensor inputs The ECM also regulates the amount of fuel injected by controlling the duration the injector remains open.

Computer controlled diesel engine management systems 37

Fig 1.37 The Rover 75 common rail diesel fuel system

Summary

The survey of computer-controlled systems reveals that key technologies such as electromagnetism, semiconductors, variable resistance, circuits, and computers are integral to the systems analyzed This highlights the common technological foundations shared across various systems Subsequent chapters will explore these foundational technologies in more depth, with Chapter 7 providing examples of tests that can assist in diagnosing faults in computer-controlled vehicle systems.

Self-diagnostic capabilities and fault codes are crucial for diagnosing computer-controlled systems, as discussed in Chapters 2 and 3 However, interpreting these codes is just the starting point; subsequent testing of sensors, actuators, and their circuits is essential for effective fault-finding This chapter highlights the shared knowledge of sensors and actuators applicable across various systems A deeper exploration of their operating principles is provided in Chapters 5 and 6, and this foundational knowledge will be beneficial for testing multiple systems, as demonstrated in Chapter 7.

1.13 Review questions (see Appendix 2 for answers)

1 The purpose of exhaust gas recirculation is:

(a) to reburn the exhaust gas?

(b) to reduce combustion temperature and reduce NO x emissions?

(d) to give better fuel economy?

(b) shuts off current in the Hall element so that the signal voltage is zero when the magnetic field is blocked?

(c) gives an increase in signal current as the speed increases?

(d) is only used in ignition systems?

(a) the computer uses the peak-to-peak voltage from the wheel sensor to control braking?

(b) the computer compares frequencies from wheel sensors to help control braking?

(c) the warning light will go out when the vehicle speed reaches 50 km/h? (d) the braking distance is greatly reduced in all conditions?

4 In sequential multi-point petrol injection systems there is one injection of fuel to each cylinder:

(a) on each stroke of the piston?

(b) each time a piston approaches TDC on the exhaust stroke?

(c) whenever hard acceleration takes place?

(d) when the knock sensor transmits a signal?

5 The manifold absolute pressure sensor is used in speed density fuel injection systems to:

(a) provide a signal that enables the ECM to calculate the amount of fuel entering the engine?

(b) provide a signal that enables the ECM to calculate the amount of air entering the engine?

(c) control the fuel pressure at the injectors?

(a) is a procedure that allows the ECM to set new values for certain operating variables as the system wears?

(b) is a limited operating strategy that allows the ECM to set values that will get a vehicle back to the workshop for repair?

(c) alters map values in the ROM?

(d) is a procedure for fault tracing?

(a) the fuel and air are mixed in the intake manifold?

(b) ignition is caused by glow plugs?

(c) the heat generated by compression causes combustion to take place? (d) a mixture of fuel and air is forced into the cylinder by the injector?

(a) the ECM changes the damping rate to suit driving conditions?

(b) the steering angle sensor is fitted to the front wheel drive shafts?

(c) the system must not operate at speeds greater than 25 km/h?

(d) the ECM learns a new set of values if a suspension spring breaks?

Vehicle computers (ECMs) are not designed for repair in garage workshops, yet technicians must understand computer technology due to the significance of diagnostic trouble codes (DTCs) stored in the computer memory The method for reading DTCs varies by vehicle, making it essential for technicians to recognize that procedures may differ across models Additionally, technicians at main dealer workshops often utilize specialized equipment to modify the computer's operating program The increasing use of 'freeze frame' data, which captures live data during operation, aids in diagnosing system faults While 'user-friendly' diagnostic tools facilitate these tasks, a solid understanding of ECM capabilities remains valuable for technicians.

The fundamental parts of a computer

COMPUTER MEMORY

Read-Only Memory (ROM) is a crucial component in computers, housing the operating program essential for functionality It is comprised of electronic circuits that produce specific outputs based on predetermined input values, ensuring reliable performance Additionally, ROMs are designed with a substantial storage capacity, making them vital for system operations.

Random Access Memory (RAM) is a type of temporary storage that holds data while the processing unit is actively working on it The act of storing data in RAM is known as 'writing,' while utilizing that data is referred to as 'reading.'

THE CLOCK

A clock in a computer is an electronic circuit that leverages the piezoelectric effect of a quartz crystal to generate precise electrical pulses, which regulate the computer's operations Clock speeds are quantified by the number of pulses produced per second, with 1 Hertz (Hz) representing one pulse per second Most computer clocks function at millions of pulses per second, with 1 megahertz (1 MHz) equating to one million pulses per second.

A practical automotive computer system

Figure 2.2 shows a computer controlled transmission system At the heart of the system is an electronic module This particular module is a self-contained

A computer-controlled transmission system utilizes a microcontroller, which comes in various sizes such as 4, 8, 16, and 32 bits, indicating the length of the binary code it processes The system in question features an 8-bit microcontroller, and Figure 2.3 provides a glimpse into its internal workings, offering insights into its operational mechanisms.

This is an 8-bit microcontroller In computer language a bit is a 0 or a 1 The 0 normally represents zero, or low voltage, and the 1 normally represents a higher voltage, probably 1.8 V.

The microcontroller integrated circuit features a ROM capacity of 2048 bytes and a RAM capacity of 64 bytes, with each byte consisting of 8 bits Additionally, it is equipped with the capability to convert four analog inputs into 8-bit digital codes.

The power supply is a circuit that takes its supply from the vehicle battery then provides a regulated d.c supply of 5 V to the microcontroller, and this is its

The internal details of a computer's working voltage include a power supply equipped with protection mechanisms against both overvoltage and undervoltage Specifically, undervoltage protection is crucial when battery voltage drops, typically implemented using a capacitor.

In this application, the clock functions at a frequency of 4 MHz, overseeing the computer's operations It counts sensor pulses to measure speed and regulates output pulses to the electrovalves, ensuring that gear changes occur smoothly and at the precise timing needed.

The input interface features electronic circuits that supply electrical power to connected sensors and switches Some inputs are in an analogue format, which cannot be directly interpreted by the computer; therefore, these signals must be converted into digital form at the interface for proper processing.

The power driver consists of power transistors that are switched electronically to operate electrovalves that operate the gear change hydraulics.

At (6) on the diagram the inscription reads ‘ Reading electrical state’ This means that the computer is being made aware of the positions (on or off) of the electrovalves.

The watchdog circuit is a timer circuit that prevents the computer from going into an endless loop that can sometimes happen if false readings occur.

The diagnostic interface is a circuit that causes a warning lamp to be illuminated in case of a system malfunction It can also be used to connect to the diagnostic kit.

Principles of operation

Automotive computer-controlled systems depend on sensor inputs to function effectively The onboard computer analyzes these inputs against predefined values stored in its program memory (ROM) to decide the appropriate signals for actuators, specifically electrovalves, facilitating seamless gear changes.

This application utilizes the concept of the vehicle operating point, which is influenced by two key sensor inputs: vehicle speed and load Vehicle speed is measured using an electromagnetic sensor, while load is assessed through the throttle position sensor For more detailed information about these sensors, refer to Chapter 5.

The vehicle's ROM stores a set of operating points that serve as references for gear changes during operation When the speed sensor detects that the vehicle's speed exceeds the predefined value in the ROM, the computer initiates a shift to a higher gear Conversely, if the vehicle speed drops below the ROM's specified level, a downshift to a lower gear is requested.

If a microcomputer identifies three consecutive sensor readings that exceed predefined limits, the fault detection system activates This system is capable of detecting various types of failures, including electrohydraulic valve malfunctions and throttle position sensor issues.

Computer data 45 ž speed sensor failure ž power source (battery) voltage failure.

When a failure is detected, warning lamps illuminate, activating the 'limp home' feature, and a diagnostic code is likely stored in RAM for future analysis.

The 'limp home' mode is a computer subroutine designed to allow a vehicle to operate in high gear, enabling the driver to reach a service garage for necessary repairs.

Computer data

DATA TRANSFERS

Coded data is transmitted as electrical pulses within a computer and between connected computers For instance, the number 20 is represented as 0001 0100 in 8-bit binary and is sent via a parallel bus consisting of eight adjacent wires This method of transmission is referred to as parallel data transmission.

8 Wires side by side Parallel

0 0 Whole word in one go

Serial data transmission involves sending data bits (0s and 1s) sequentially along a single wire in networked systems The transmission speed is quantified by the number of bits sent per second, referred to as the 'Baud' rate, named after its originator This method allows for efficient communication of digital information, as illustrated in the accompanying diagram.

DATA TRANSFER REQUIREMENTS

In order for the computer controlled systems to function correctly certain require- ments must be met.

1 There must be a method that enables the computer processor to identify a specific device’s interface from all other interfaces and memory devices that are attached to the internal buses of the computer.

2 There must be a temporary storage space (buffer) where data can be held (if necessary) when it is being transferred between the computer processor and a peripheral, such as a sensor or an actuator.

3 The peripherals, such as speed sensors and fuel injectors, must supply status information to the computer processor, via the interfaces, to inform the computer processor that they are ready to send data to it, or receive data from it.

4 The computer must generate and receive timing and control signals that are compatible with the computer’s processor These timings and signals must also be compatible with the sending or receiving device, i.e the sensor or actuator.

5 There must be a means to convert the sensor signals into digital data that the computer can use and also a means to convert digital data into a form that the actuators can use.

Computer interfaces

The interface connecting computers to peripherals like sensors and actuators typically relies on a single chip integrated circuit An example of this is illustrated in Figure 2.5, showcasing the Motorola MC6805 ACIA (asynchronous communications interface adaptor).

The blocks marked R1 and R2 are shift registers R1 receives a data word as

The system converts 8 parallel bits into a serial bit stream, which R2 then receives and transfers back to the bus as an 8-bit parallel word The control logic circuit is managed by the computer, while the 8-bit bus at the top left facilitates communication between the control unit and various internal circuits of the microcontroller.

Control of output devices

In many cases the commands from the computer are used to connect a circuit to earth, via a transistor Two methods are used; one method is known as

The duty cycle and pulse width modulation are two distinct methods that generate unique voltage patterns, which can be analyzed using an oscilloscope These patterns are visually represented in Fig 2.6.

Duty cycle control allows a transistor to operate a device either continuously (100% of the time) or for a limited duration, such as 30% This method regulates the device's performance by adjusting the duration of its "on time." For instance, a duty cycle of 50% indicates that the device, like a petrol injector or mixture control valve, is active for half of the available time.

Pulse width modulation (PWM) enables the transistor to switch on and off at high frequencies, effectively minimizing the heating effect in the solenoid of the operating device, such as an injector.

Fig 2.6(a) Duty cycle control of a mixture control solenoid

Fig 2.6(b) Pulse width modulation applied to a fuel injector

Computer memories

READ ONLY MEMORIES

The system's controlling program is stored in read-only memory (ROM), which comes in various types utilized in automotive computers Understanding the differences between these ROM types is crucial, as a service procedure applicable to one vehicle make may not be effective for a similar model due to these variations in ROM.

Figure 2.8 illustrates a block diagram of a compact ROM circuit, accompanied by a truth table detailing the output values on lines F0 to F3 The output is determined by the electrical inputs A, B, and C; specifically, when these inputs indicate logic 0, the corresponding output values for F0 to F3 are generated.

Fig 2.8 A ROM circuit and truth table

ROMs come in different types, with most main program memory being non-modifiable once configured unless the integrated circuit is replaced However, certain vehicle computers utilize ROM types that can be altered during service, but only by authorized personnel The ROM in the Engine Control Module (ECM) stores the essential program that regulates system operations, and any unauthorized tampering could lead to severe consequences.

Mask programmable ROM is commonly utilized in large-scale manufacturing due to its fixed nature after configuration The term "mask" pertains to the stencil used during the construction of the ROM's electronic circuit, ensuring that once programmed, the ROM cannot be modified.

Programmable ROMs, often known as field programmable ROMs, allow for circuit modifications outside of a factory setting These memory circuits feature fusible links that can be selectively blown using a PROM programmer Once these links are broken, they cannot be restored, making the programming process permanent.

Electrically programmable read-only memories (EPROM) are specialized memory circuits that retain data through an electrical charge storage mechanism, such as a capacitor, even when power is disconnected These memory chips can be erased by exposure to ultraviolet light, often indicated by a small window in the chip housing that is typically covered Once erased, EPROM can be reprogrammed electrically, making it a versatile option for data storage.

An electrically erasable PROM (EEPROM) operates similarly to EPROM, with the key distinction being its ability to be erased and reprogrammed through a dedicated charge pump circuit This circuit is managed by the microcontroller in accordance with the ECM's operational program.

RANDOM ACCESS MEMORY

Random Access Memory (RAM) is a crucial component of a computer, serving as temporary storage for data actively being processed It is a type of read-and-write memory, allowing data to be both written to and read from, which results in constantly changing contents during operation RAM is powered by electricity, and its volatile nature means that all stored information is lost when the power supply is interrupted.

OTHER TYPES OF COMPUTER

Hard discs consist of magnetizable material organized in circular tracks, where magnetized areas signify '1's and non-magnetized areas represent '0's in computer language As the disc spins past a read-and-write head, the magnetism is transformed into electrical signals, which generate the data that powers the computer Capable of storing millions of bits of data, hard discs offer significantly greater storage capacity compared to floppy discs, which function on similar principles but with limited capacity.

Compact discs (CDROMs) offer significant storage capacity, resembling traditional gramophone records with their variable groove depths A laser reads these grooves, detecting the differences in depth to access the stored data efficiently.

The ECM 51 beam operates with an adaptive strategy, integrating seamlessly with an electronic circuit that transforms laser readings into voltages These voltages correspond to binary values, 0s and 1s, which are essential for computer processing.

Fault codes

A microcontroller in an automotive system, like engine management, continuously monitors various sensor readings These readings are compared to values stored in the program's ROM When the sensor readings align with the programmed values, the microcontroller determines the necessary outputs to actuators, such as fuel injectors.

If a sensor reading falls outside the specified limits, it will be re-evaluated Should the reading remain out of limits, a fault code will be recorded in a designated section of RAM.

Designers often program microcontrollers to enable systems to function under various criteria until repairs are completed or faults are resolved Diagnostic trouble codes (DTCs) are crucial for service technicians, necessitating a clear understanding of access procedures It's important to note that if DTCs are stored in standard RAM, they will be lost when the ECM power is turned off, which is why different methods for preserving these codes are implemented.

Keep Alive Memory (KAM) describes systems where the Engine Control Module (ECM) maintains a continuous, fused power supply, allowing it to retain fault codes as long as battery power is available.

EEPROMs are utilized for storing fault codes and data associated with vehicle system events, retaining this information even when power is lost For a detailed discussion on fault codes, refer to Chapter 3.

Adaptive operating strategy of the ECM

LIMITED OPERATING STRATEGY (LOS)

When a non-critical engine defect arises, the ROM program typically activates a 'limp home mode' that enables the vehicle to be driven to a service location It's important to recognize that any efforts to address the defect must consider the system's restricted operating condition.

Networking of computers

A BUS-BASED SYSTEM

Figure 2.10 shows the basic principle of a number of computers which are linked together by a common wire along which are sent the messages that the computers use to share data.

One significant benefit of this system is its ability to minimize the number of required wires; however, issues may arise if multiple messages are transmitted simultaneously on the data bus This challenge is addressed by implementing strict protocols that govern the transfer of data between the connected computers.

STAR CONNECTED COMPUTERS

An alternative to the bus system of connecting computers together is the star system shown in Fig 2.11 An advantage of this system is that a break in the

Fig 2.10 A simple bus-based network of computers

In a star-connected computer network, the failure of one computer does not disrupt the entire system The central hub, which can function as an electronic switch, receives messages from various computers and identifies the intended recipient among the connected devices It then forwards the message exclusively to the designated computer, ensuring efficient communication within the network.

Networked computer systems are commonly integrated into vehicles, utilizing the Controller Area Network (CAN), a high-speed networking system developed by Bosch for automotive applications It’s important to note that "high speed" pertains to the data transfer rate within the network rather than the vehicle's speed When vehicles feature networks with varying baud rates, they typically communicate through an interface designed for this purpose.

MESSAGES

A message refers to a data item transmitted from one computer (ECM) to another over a network It can vary in size, ranging from extensive files of several megabytes to brief pieces of data consisting of just a few bytes.

To optimize data transmission and avoid delays, long messages are segmented into smaller units known as packets This method ensures that each packet is transmitted individually over the network bus, allowing the receiving computer to efficiently reassemble them into the complete message By using packets, urgent communications can be prioritized without interference from longer transmissions.

(Note, 1 baudD1 bit, binary 0 or 1, per second.)

Before transmission, a packet is organized into a frame that includes the packet itself, additional error detection bits, identification data for the sending computer, destination recognition data, a sequence indicating the start of the frame, and bits that denote the frame's length or its conclusion.

Each computer on the network has a unique network address.

PROTOCOLS

For networks to operate effectively, they require protocols that regulate data transfer One widely utilized protocol for communication among networked computers is carrier-sense multiple access with collision avoidance (CSMA-CD) This protocol ensures efficient data transmission by managing how devices access the network and avoid collisions.

In a network, a computer must wait for idle conditions to transmit a frame Once transmitted, all computers verify the destination address, and the intended recipient accepts the complete frame The destination then performs an error check; if an error is found, it sends an error message back to the sender Upon receiving this error notification, the transmitting computer will re-send the entire frame.

When two computers transmit a frame simultaneously on a bus, a collision occurs, leading to frame corruption In response, the protocol mandates that the transmitting computers cease transmission immediately and send a jamming signal to alert other network devices This jamming signal prompts all computers to disregard the corrupted frames, and each must wait briefly before attempting to retransmit.

Every device connected to a network requires an appropriate interface This interface circuit card contains a microprocessor that enables it to receive and verify data frames, allowing the main processor of the computer to continue its tasks without interruption.

To summarize, in order for a local area network (LAN) to function the following must happen:

Vehicle network systems require the division of data into packets, which must include error detection bits Each packet is then structured into a frame for transmission over the network To ensure reliable communication, collision detection is essential; if a collision occurs, transmission halts, and a jamming signal is issued Afterward, computers must wait a random period before attempting to transmit again.

It should be noted that this all takes place in microseconds under the control of the computer clock.

Vehicle network systems

THE PRINCIPLE OF A BUS-BASED

In vehicles, the controls for nearly all systems are designed to be positioned close to the driver's seat, ensuring easy access This setup typically involves standard wiring, which consists of one cable delivering electrical power to the switch and another cable carrying the electricity from the switch to the respective unit being operated.

The rise in electrically-operated equipment in vehicles has led to a significant concentration of electrical cables near the driver's position, creating challenges such as limited space for wiring and potential defects from extra cable connectors Multiplexed or data bus-based systems provide effective solutions to these issues.

Figure 2.12 illustrates the fundamental concept of multiplexed vehicle wiring, emphasizing the core idea while intentionally omitting components like fuses for simplicity.

1 & 2 Electronic switches for side and tail lights.

3 Electronic switch for head lights.

4 Electronic switch for rear window demister.

A, B, C & D Dash panel switches for lights etc.

Fig 2.12 The multiplexed wiring concept

The broken line in the diagram symbolizes the data bus, which serves as the electrical conductor that transmits messages to the corresponding remote control units These messages consist of digital data represented by 0s and 1s.

The electronic interface, represented by rectangles 1, 2, 3, and 4, enables two-way communication between the ECU and components like lamps and the heated rear window Dash panel switches connect to a multiplexer (MUX), allowing binary codes to convey various switch combinations to the ECU, which then transmits this information onto the data bus For instance, activating the side and tail lamps while keeping other switches off generates a binary code of 1000, along with additional bits required by the protocol, to power the side lamps Similarly, engaging the heated rear window generates a different binary code that the ECU sends to the data bus.

As the processor is moving the data bits at a rate of around 10 000 per second it is evident that, to the human eye, any changes appear to occur instantaneously.

DATA BUSES FOR DIFFERENT

The traction control system functions in real-time, requiring rapid data exchange between its components Increasingly, the Controller Area Network (CAN), developed by Bosch and classified as SAE Class C, is utilized for such systems CAN employs a two-wire twisted pair for efficient data transmission.

The Rover 75 is a modern vehicle that uses several different data buses, as described below.

1 A two-wire CAN bus that can operate at high data transmission speeds of up to

Fig 2.13 The CAN bus system

2 A single-wire bus for doors, lights, sun roof etc This bus operates at a data speed of 9.6 kbaud (Fig 2.14).

3 A single-wire bus for diagnostic purposes This bus operates at 10.4 kbaud (Fig 2.15).

The twisted pair of the CAN bus system minimizes electrically-initiated interfer- ence and virtually eliminates the possibility of messages becoming corrupted.

ENCODING SERIAL DATA

In addition to the protocols outlined in section 2.10.4, it is essential to explore practical methods for transmitting messages across data buses Key considerations include transmission speed (bit rate), electrical interference, and message integrity Two prevalent transmission methods are non-return to zero (NRZ) and controller area network (CAN).

The distinctions between various methods of representing logic levels in computing primarily involve how binary values (0 and 1, or high and low) are conveyed For instance, the NRZ method transmits a binary sequence, such as 0,1,1,1,0,0,1, in a specific format, as illustrated in Fig 2.16.

Parking aid Sunroof Rain sensor

High line bord monitor switch interface Telephone

Fig 2.14 The single wire BMW K bus

Fig 2.15 The single wire diagnostic bus

The point to note is that each bit is transmitted for one bit time without any change.

In a Controller Area Network (CAN), data transmission occurs through two wires: CAN-high (CAN-H) and CAN-low (CAN-L) A visual representation of a CAN bit sequence is illustrated in Fig 2.17.

Fig 2.16 NRZ transmission of a binary bit sequence

The CAN-H wire operates between 2.5 and 3.5 V, while the CAN-L wire ranges from 2.5 to 1.5 V A voltage of 2.5 V on both wires indicates a logic 0, as there is no voltage difference Conversely, a logic 1 is established when there is a 2 V difference, achieved when CAN-H reaches 3.5 V and CAN-L drops to 1.5 V.

Prototype network systems

To enhance understanding of vehicle system networking, we examine a concept vehicle developed by LucasVarity, illustrated in Figure 2.18 This networked system, applicable to various vehicles such as trucks and buses, integrates four key subsystems, including traction control and stability control, showcasing its versatility and functionality.

1 The Lucas EPIC electronically-programmed injection control system, which is a computer controlled engine management system for diesel engines, similar to the one described in section 1.11.

The Lucas flow valve anti-lock braking system features an innovative design that includes a second solenoid valve at each front wheel This allows for independent brake application, utilizing the ABS pump to generate the necessary pressure for enhanced braking control.

3 A clutch management system (CMS) This replaces the normal clutch pedal linkage with a computer controlled, hydraulically actuated system The manual

The LucasVarity advanced prototype vehicle features a gearshift system that eliminates the need for a clutch pedal, allowing for two-pedal control Drivers are still required to lift their foot from the accelerator when changing gears, which helps maintain fuel efficiency without the drawbacks of automatic transmission This innovative design ensures that drivers retain complete control over gear change operations.

4 Adjustable rate dampers are fitted The damping rate is adjusted by the computer (ECM) to provide optimum damping during rapid steering input, braking and acceleration.

Each subsystem is equipped with a CAN interface that enables connectivity to the master controller Twisted pair cables form a network linking these subsystems to the master controller, facilitating the reliable transfer of sensor data and control signals while ensuring safety and minimizing wiring Consequently, the master controller gathers information from the subsystems through the CAN bus cables.

The master controller is linked to a switch pack for cruise and damper control, along with two accelerometers and an inclinometer for hill detection, enabling it to fully understand the vehicle's status and the driver's needs It processes this information to create control signals that override the normal functioning of subsystems, ensuring optimal vehicle performance.

Prototype network systems 61 another tier of systems known as the integrated systems In the event of CAN failure, each subsystem defaults to stand-alone operation.

The four integrated subsystems—EPIC, ABS, damper control, and clutch management—work together through the master controller to enhance vehicle management by providing seven essential functions These functions include traction and stability control, cruise control, power shift, engine drag control, hill hold, damper control, and centralized diagnostics.

The ABS wheel speed sensor provides crucial information to the ABS computer regarding wheel-to-surface conditions When a vehicle is moving at low speeds or when only one wheel spins—like when one wheel is on ice and the other on dry pavement—the system automatically applies the brake to the spinning wheel Conversely, at higher speeds or when both wheels are spinning, the engine power is reduced to prevent wheel spin This dual approach enhances traction, improves acceleration, and ensures safer cornering at elevated speeds.

The vehicle speed sensor plays a crucial role in engine control (EPIC) by helping to maintain the driver's selected speed The cruise control switch pack allows the driver to set the desired speed and easily toggle the system on and off as needed.

The power shift function enhances driving convenience by automatically reducing engine power during gear changes, allowing drivers to shift gears without lifting their foot from the accelerator This feature simplifies the synchronization of accelerator and gear lever movements and can also include throttle 'blipping' for smoother downshifts.

This system prevents wheel locking caused by engine braking on slippery surfaces, enhancing anti-lock braking performance By slightly increasing engine power, it minimizes engine drag to maintain optimal wheel slip for effective deceleration and stability In critical situations, disengaging the clutch eliminates engine inertia, enabling faster wheel response to anti-lock brake control, which improves steering ability and shortens stopping distances.

Hill hold technology automatically engages the rear brakes when a vehicle stops on an incline, preventing roll back Upon restarting, it utilizes data from the inclinometer sensor, EPIC system, ABS controller, and clutch management controller to determine the optimal moment for brake release, ensuring a smooth and seamless pull away.

The damper control system utilizes data from the CAN data bus to adjust damping rate settings, ensuring optimal performance For enhanced responsiveness during rapid steering, braking, and acceleration, the dampers are switched to a 'firm' setting When returning to normal cruising conditions, the system selects a 'soft' damper setting to improve ride comfort.

Centralized diagnostics utilize a master controller to oversee all networked systems, interpreting data bus information to identify and respond to faults in subsystems and network communications This approach ensures fail-safe operation and accurate fault recognition The diagnostic section features an interface that allows the Lucas Laser 2000 interrogation tool to access vital diagnostic information Future enhancements are expected to incorporate electronic power-assisted steering, electronic braking, and active anti-roll bars.

Summary

Understanding data bus communication is crucial for vehicle repair technicians, even though it primarily concerns designers Familiarity with serial data terminology can significantly aid technicians in selecting appropriate diagnostic equipment Manufacturers ensure their tools are compatible with vehicle diagnostics, and technicians benefit from knowing the relevant specifications This knowledge is essential when arranging demonstrations of equipment capabilities, which is a vital step in the purchasing process.

Review questions

(a) requires a separate wire for each bit that is transmitted between the computer and a peripheral such as a fuel injector?

(b) is faster than parallel transmission of the same data?

(c) is transmitted one bit after another along the same wire?

(d) is not used in vehicle systems?

(a) a data bus is used to carry signals to and from the computer to the remote control units?

(b) each unit in the system uses a separate computer?

(c) more wire is used than in a conventional system?

(d) a high voltage is required on the power supply?

3 In networked systems messages are divided into smaller packages to:

(a) prevent problems that may arise because some messages are longer that others?

(b) avoid each computer on the network having to have an interface?

4 When DTCs are stored in an EEPROM:

(a) the DTCs are removed when the vehicle battery is disconnected?

(b) an internal circuit must be activated to clear the fault code memory? (c) they can only be read out by use of a multimeter?

(d) they can only be removed by replacing the memory circuit?

(b) is not networked because it does not need to work with other systems on the vehicle?

(c) is not used on front-wheel drive vehicles?

(d) can only operate on vehicles equipped with a differential lock?

6 The computer clock is required:

(a) to permit the time of day to be displayed on the instrument panel?

(b) to allow the time and date to be stored for future reference?

(c) to create the electrical pulses that regulate the flow of data?

(d) to generate the voltage levels required for operation of a data bus?

(a) a ‘twisted pair’ of wires is used so that the correct length of cable can be placed in a small space?

(b) a ‘twisted pair’ of wires is used to provide the two different voltage levels and minimize electrical interference?

(c) the ‘twisted pair’ of wires carries the current that drives the ABS modu- lator?

(d) it is used only for the engine management system?

8 The RAM of the ECM computer is:

(a) the part of memory where sensor data is held while the system is in operation?

(b) only used for storing of fault codes?

Self-diagnosis and fault codes

A computer-controlled system continuously monitors the electrical state of input and output connections at the ECM interfaces, enabling the processor to compare input values with programmed values stored in ROM This capability allows the ECM to understand the system's status effectively For instance, if a throttle position sensor's reading does not align with the engine speed and load signals, the ROM software can redirect the process to an alternative program loop Consequently, a fault code, or diagnostic trouble code (DTC), is stored in a designated section of RAM for troubleshooting purposes.

DTCs serve as a crucial resource for diagnosing issues in vehicles, highlighting the importance of utilizing available methods to access this information Notably, there are tools that allow real-time readings from the ECM to be displayed on an oscilloscope during operation, or stored for future analysis and review.

Access to DTCs

METHOD 1: THE DASHBOARD LAMP

The system under examination is the Toyota electronic fuel injection system (EFI) shown in Fig 3.1.

The fuel system in the 4A-GE engine, a 1600 cc, 16 valve, 122 bhp powerhouse, is utilized in the Toyota Corolla GT Hatchback (AE82) from 1985 to 1987 Equipped with an ECU that features built-in self-diagnosis, the system can identify issues and alert the driver through the 'check engine' warning light, conveniently located on the instrument panel.

When the ignition is activated, the engine check light illuminates; it should turn off once the engine starts if there are no issues However, if the light remains on, it indicates a fault that needs attention To diagnose the problem, the system must be put into diagnostic mode, which involves specific preliminary steps.

1 (a) Check that the battery voltage is above 11 V.

(b) Check that the throttle valve is fully closed (throttle position sensor switch points closed).

(c) Ensure that transmission is in neutral position.

(d) Check that all accessory switches are off.

(e) Ensure that engine is at its normal operating temperature.

2 Turn the ignition on, but do not start the engine.

3 Using a service wire connect together (short) the terminals T and E1 of the

[Note that the ‘check engine’ connector is located near the wiper motor (AE) or battery (AA), these being different vehicle models.]

4 Read the diagnostic code as indicated by the number of flashes of the ‘check engine’ warning light.

Fig 3.1 Electronic fuel injection system

Fig 3.3 Engine diagnostic lamp on the instrument panel

Fig 3.4 Making the diagnostic output connection

Diagnostic code number 1, indicated by a single flash every 3 seconds, signifies that the system is operating correctly, appearing only when no other fault codes are present In contrast, the 'check engine' lamp blinks a specific number of times corresponding to the displayed fault code, with two rapid blinks (1 second apart) representing code 2 For further details, refer to Figure 3.6, which illustrates the fault codes for code 2 and code 4.

To indicate fault code 4, the system will pause for 3 seconds followed by four blinks This fault code will persist as long as the ‘check engine’ connector terminals (T and E1) remain connected If multiple faults are detected at once, the display will start with the lowest fault code and progress sequentially to the higher numbers.

Figure 3.7 illustrates a segment of the Toyota workshop manual that details diagnostic codes Each code corresponds to a specific section of the system, and the 'See page' column directs users to the relevant section of the manual for additional diagnostic assistance.

After completing the diagnostic check, it is essential to disconnect the 'service wire' from the 'check engine' connector and clear the diagnostic code Once the fault is fixed, the diagnostic code stored in the ECU memory must be erased, which for this Toyota model involves removing the correct fuse The fuse should be taken out for at least 10 seconds, or longer if the ambient temperature is low, with the ignition turned off.

Fig 3.5 Diagnostic code number 1 (system normal)

Fig 3.6 Diagnostic codes for codes 2 and 4

Fig 3.7 Diagnostic codes as given in a Toyota workshop manual

METHOD 2: FAULT CODES DISPLAYED

Figure 3.8 shows the circuit, and details of the method that can be used to obtain fault codes, from a Wabco braking system.

The procedure, as taken from the Wabco publication ‘Blinkcode for Goods Vehicles and Buses ABS/ASR ‘‘C’’-Generation’ gives the procedure as follows.

1 In the case of a vehicle not having an ASR lamp installed: connect a filament bulb (2W .5W) to pin 3 of the ECU (see top circuit diagram) This can be achieved using Wabco inter-adaptor installed between ECU and ECU connector (Ignition:OFF!).

2 By connecting pin 14 to vehicle ground (earth) for longer than 5 seconds this can be achieved via the switch on the inter-adaptor (Ignition:ON!).

3 The blinkcode can be read and noted until the user is in no doubt as to the transmitted fault code! The fault code can be erased by disconnecting pin 14 from vehicle ground during the blinkcode transmission.

To avoid unintentional deletion of fault codes, ensure the ignition is off during blinkcode transmission Repair any existing faults before reading additional codes After each repair, reactivate the blinkcode to confirm no further issues and clear the ECU's fault memory Once all faults are addressed and erased, the 'System OK' code (X-0-0) will be transmitted.

After each repair the system operation should be further verified by a test drive during which the ABS and ASR lamps should extinguish once the vehicle has reached 7 km/h.

The blinkcode frame is made up as shown in Fig 3.9.

METHOD 3: FAULT CODE READERS

Fault code readers vary in complexity from inexpensive devices that read out flash codes, such as the Gunson ‘Fault Finder’ shown in Fig 3.10, to

The external lamp circuit for reading blink codes in microprocessor-based machines is illustrated in Fig 3.8 Various suppliers, including Gunson, offer similar machines, which will be discussed in the following chapter.

The aim here is to give a reasonable description of the work involved in obtaining diagnostic information through the serial port In effect, one connects

Fig 3.9 The fault code frame for the Wabco system

The Gunson ‘fault finder’ is a fault code reader that allows users to troubleshoot issues by following the instructions provided in the handbook and displayed on the instrument's panel This article will delve deeper into the operational details to enhance understanding of its functionality.

The diagnostic kit, as illustrated in Figure 3.11, comprises essential components including a handheld tester, a connecting lead for the vehicle’s diagnostic port, a smart card for vehicle system compatibility, a printer for recording test results, and additional leads for battery and printer connections Accompanied by an instruction manual (Figure 3.12), the tester also features a user-friendly display screen that offers a step-by-step menu to assist operators throughout the testing process.

The ‘smart card’ is the equivalent of computer software and it enables the tester to use the ECM processor power to interrogate circuits The test instrument

Fig 3.11 The diagnostic kit (scan tool)

The instruction manual allows for the testing of all circuits connected to the ECM through the serial port, which transmits test information serially, bit by bit (e.g., 10110011) This serial port offers a significant advantage by enabling testing without the necessity of disconnecting any wiring.

If the operator is not familiar with the vehicle, consulting a location chart is essential to find the diagnostic connector For instance, Figure 3.13 illustrates the connection point for the Rover 200 series.

The tester derives its power from the vehicle battery, as illustrated in Fig 3.14, which depicts the connection of the leads While the tester is positioned for photography, it is typically held in hand during testing It is essential to ensure that the instrument is placed safely when not being actively held.

To initiate the diagnostic process, connect the diagnostic lead to the vehicle's diagnostic connector, as illustrated in Fig 3.13 Before starting the test, ensure that the appropriate diagnostic lead for the specific vehicle model has been selected, along with the smart card that customizes the test instrument for the vehicle, as shown in Figure 3.15.

It will be understood that different makes of vehicle require different types of diagnostic leads and smart cards This is necessary because the diagnostic

Fig 3.14 Connecting to the power supply

Fig 3.15 Inserting the ‘smart’ card to adapt the test instrument to the specific vehicle application

The diagnostic lead and smart card for Ford vehicles vary by model, as does the associated test program These tools, depicted in Figure 3.16, customize the test instrument for specific Ford vehicles A diverse selection of diagnostic leads and smart cards is available, ensuring compatibility with various vehicle makes This flexibility is crucial for independent garages that service multiple brands, as they are not tied to a single vehicle manufacturer.

An essential aspect of a systematic fault-finding approach is the collection of evidence As illustrated in Figure 3.17, connecting the printer allows for the generation of a permanent record of test results, which can be seen in Figure 3.18.

Before commencing the test, ensure all leads are properly connected and clear of drive belts and hot engine components The manual (Fig 3.12) details the instrument controls, and once preparations are complete, the test instrument screen will display a message to guide the operator through the testing sequence.

During the test procedure, the operator must engage specific vehicle controls, as illustrated in Figure 3.19, which depicts the accelerator being pressed This highlights the necessity for some movement within the vehicle throughout the testing sequence.

To ensure safety and efficiency, it is crucial to prevent leads from becoming tangled and to position the vehicle in a way that allows for unobstructed movement around it.

Fig 3.18 The permanent copy of the test results

After the test is completed, a printout is generated for result analysis Once diagnostic and repair tasks are finished, the fault code is cleared by following the on-screen instructions The instrument is then detached, and the vehicle is readied for a road test to confirm the effectiveness of the repairs.

Fig 3.19 Operating the vehicle controls during the tests

Developments in self-diagnosis

OBD I

Since 1988, vehicles have been mandated to include electronically controlled systems that monitor their performance Any issues impacting exhaust emissions must trigger a warning light, known as the malfunction indicator lamp (MIL), on the dashboard Furthermore, these malfunctions are recorded in the engine control module's (ECM) memory and can be accessed using onboard diagnostic tools, such as a flash code displayed on a lamp.

OBD II

OBD II strengthens the requirements of OBD I on vehicles of model year 1994 and afterwards OBD II applies to spark-ignition cars and light vans, and from

Since 1996, diesel-engined vehicles have required continuous monitoring of key emissions-related systems These systems include combustion, catalytic converters, oxygen (lambda) sensors, secondary air systems, fuel evaporative control systems, and exhaust gas recirculation systems.

The requirements for diesel-engined vehicles vary and glow plug equipment may be monitored instead of the catalytic converter.

OBD II features include a malfunction indicator lamp (MIL) with a flashing function, the ability to read diagnostic trouble codes (DTCs) using a standard scan tool through a 16-pin diagnostic connector, and the requirement to monitor emissions-related components for compliance with emissions limits as well as defects Additionally, operating conditions and performance data can be logged and stored in a 'freeze frame' for further analysis.

Pin 7 and 15: Data transfer in accordance with DIN ISO 9141-2

Pin 2 and 10: Data transfer in accordance with SAE J 1962

Pin 1, 3, 6, 8, 9, 11-14 are not assigned to CARB.

(OBD II data administration guideline "OBD II-DV") Pin 4: Vehicle ground (body)

Pin 5: Signal ground Pin 16: Battery positive

Fig 3.20 The SAE J 1962 standardized diagnostic link connector (DLC)

Fig 3.21 The structure of standard fault codes for OBD II

Diagnostic equipment and limitations of DTCs 81

The malfunction indicator lamp (MIL) should illuminate briefly when the ignition is turned on, indicating that the engine control module (ECM) is conducting self-checks It should turn off after about three seconds and only activate again if a malfunction occurs while the engine is running If the MIL does not light up during the initial ignition phase, it suggests a fault either in the MIL or the ECM, provided that the battery is functioning properly.

From the perspective of repair shops, OBD II offers significant advantages, including a standardized diagnostic interface and connector, as well as uniform fault codes These fault codes, displayed on the scan tool, consist of five digits, such as P0125 The first digit indicates the vehicle system, the second digit specifies the subgroup, the third digit denotes the subassembly, while the fourth and fifth digits pinpoint the localized system components.

Figure 3.21 shows how a range of fault codes can be constructed by using the recommended standard approach.

The code P0125 indicates 'insufficient coolant temperature for closed loop fuel control' within its coding system For a comprehensive understanding of this and many other codes, refer to the SAE J 2012 publication, which contains extensive details on hundreds of diagnostic codes.

Diagnostic equipment and limitations of

While it may seem that new tools are required for OBD II and EOBD diagnostics, existing diagnostic equipment like the Bosch KTS300 can effectively handle fault code retrieval and analysis for both non-OBD II systems with ISO 9141 serial links and OBD II systems with appropriate adaptors Further details on this equipment can be found in Chapter 4.

Fig 3.22 The Bosch KTS300 portable diagnostic tool

Reading Diagnostic Trouble Codes (DTCs) is a crucial step in diagnosing and repairing defects, such as those indicated by a low coolant temperature signal from the coolant sensor The sensor's output is transmitted to the Engine Control Module (ECM) through a cable with multiple connectors The ECM interprets the voltage reading from the sensor circuit; however, if there is a defect, like high resistance, it may receive a voltage that inaccurately reflects a lower coolant temperature than reality.

Automotive computer-controlled systems rely on various sensors, actuators, and circuits for their operation, with Diagnostic Trouble Codes (DTCs) serving as valuable aids in fault diagnosis However, DTCs typically do not pinpoint the exact issue, necessitating additional tools and equipment to identify the root causes of faults and perform repairs For an in-depth exploration of this topic, refer to Chapter 4.

Review questions

(a) computer codes that can be displayed at a fault code reader?

(b) only readable through the serial connector of the ECM?

(c) generated at random whenever there is a fault on any part of the vehicle? (d) information that tells the user exactly what the fault is?

(a) permits the vehicle to be driven until a repair can be made?

(b) cuts out fuel injection above a certain engine speed?

(c) retards ignition timing to stop combustion knock?

(d) refers to the limited nature of fault codes for diagnostic purposes?

3 Microprocessor based diagnostic testers can:

(b) read fault codes and perform actuator tests via the serial port of the vehicle? (c) reset the values stored in a mask programmable ROM?

(d) only read out diagnostic data from CAN systems?

4 The standardized serial port for diagnostics that is used with OBD II has: (a) a 3-pin connector?

(b) no specified number of pins but its position on the vehicle is specified? (c) a 16-pin connector?

(d) no pins specifically allocated to the OBD II emissions systems?

5 In order to read out diagnostic trouble codes (fault codes) it is necessary to: (a) earth the K line and read the flashing light?

(b) carry out the manufacturer’s recommended procedure?

(d) take the vehicle for a road test first?

6 An ABS ECM should have good self-diagnostics because:

(a) the sensor output signals cannot be measured independently?

(b) it is difficult to simulate actual anti-lock conditions with a stationary vehicle? (c) if the ABS warning light comes on it will stop the vehicle?

(d) the fault codes are always stored in an EEPROM?

(a) a set of ROM data that is used in very cold weather?

(b) data that is used by the ECM when there is an emergency?

(c) a set of data about operating conditions that is placed in the fault code memory when the self-diagnostics detects a fault?

(d) a diagnostic feature of very early types of electronic control only?

(a) digit 1, at the left-hand end, identifies the vehicle system?

(b) the digit at the far-right hand end identifies the system?

(c) all computer controlled vehicle systems must use them?

(d) the identifying digits can appear in any order?

This chapter discusses various tools and equipment available to technicians for accurate and efficient automotive diagnosis and repair It does not serve as a comprehensive catalogue, as numerous companies manufacture and supply these tools, with several addresses provided in the Appendix Specific tools are highlighted as case studies based on the information supplied by their manufacturers, rather than indicating a preference for any particular brand.

4.1 Diagnostic tools that connect to the ECM

The ECM (Engine Control Module) is equipped with advanced self-diagnostic capabilities, storing valuable Diagnostic Trouble Codes (DTCs) that aid in vehicle diagnostics Its continuous monitoring of inputs and outputs allows data sharing with other computers using the same protocols This feature is essential for microprocessor-based diagnostic tools, enabling real-time system behavior analysis and data capture for further examination For effective communication between diagnostic equipment and the ECM, a suitable serial diagnostic interface is necessary, as illustrated in Fig 2.5.

The USA OBD II and California Air Resources Board (CARB) standard are gaining traction, yet the ISO 9141 standard remains prevalent in UK and European systems ISO 9141 allows technicians to connect a scan tool to the diagnostic plug, using compatible software, often stored on a smart card, to retrieve fault codes and additional data efficiently.

2000 machine, as shown in Fig 4.1, is an example of diagnostic equipment that can be used for a range of diagnostic work.

The Laser 2000 utilizes the on-board diagnostic capabilities integrated within the ECU, with varying levels of sophistication among different vehicle manufacturers This advanced machine enables several functions, including reading fault codes and providing explanatory text, monitoring live data in real-time with the option to display multiple parameters for comparative analysis, and storing up to four sets of data along with their corresponding timestamps Additionally, it features a snapshot mode that records data before and after an intermittent fault during road tests, allowing for detailed examination of abnormalities Furthermore, the microprocessor-based Laser 2000 can activate injectors and other components for independent testing.

Diagnostic tools that connect to the ECM 87

4.1.1 ACCESSING DIAGNOSTIC DATA WHEN THERE IS NO SERIAL PORT

In the UK, vehicles typically have an average lifespan of around 10 years, leading vehicle technicians to encounter various computer-controlled automotive systems, some lacking a serial diagnostic port To address this issue, the Lucas Laser machine can be modified for use with these systems by incorporating the Lucas Laser 1500, as illustrated in Fig 4.2 The Laser 1500 serves as a data acquisition unit that connects between the Engine Control Module (ECM) and the main harness connector, allowing for effective diagnostics Once the connection is established, the Laser 2000 machine can be linked to the Laser 1500, facilitating comprehensive vehicle analysis.

The Laser 1500, equipped with a computer-controlled system, can undergo a variety of tests comparable to those using a serial port To facilitate this, specific adapter cables and overlays are necessary, allowing the Laser 1500 to be compatible with multiple systems Figure 4.2 illustrates the general principle behind this adaptability.

4.1.2 OBD II TYPE DIAGNOSTIC EQUIPMENT

OBD II has long been utilized for vehicle diagnostics, with recent legislation emphasizing the importance of standardization in accessing diagnostic data and supporting documentation Consequently, certain diagnostic techniques may also be applicable to non-OBD II systems.

Firstly the principal features that relate to OBD II are outlined This is followed by a description of the equipment and its diagnostic functions The principal features are as follows.

1 A standard 16-pin SAE J 1962 diagnostics plug-in point, described in Chapter 3.

2 The diagnostic plug should be accessible from the driving seat and the preferred location is as shown in Fig 4.3.

Fig 4.3 The preferred location of the SAE J 1962 diagnostic interface

3 The communication between the scan tool and the ECM takes place according to one of a small number of protocols.

The diagnostic communication initialization occurs through the diagnostic equipment, where a hexadecimal 33 signal is sent to the ECM using a scan tool at a transmission speed of 5 baud, equivalent to 5 binary bits per second.

Diagnostic tools that connect to the ECM 89

5 The ECM then sends a ‘header label’ to the scan tool in response to the intialization prompt This header label consists of information about the baud rate and two keywords.

To verify proper communication setup, the scan tool inverts the second keyword and transmits it back to the ECM, where inversion in binary language entails switching 0s to 1s and 1s to 0s.

7 The ECM sends the inverted memory address (hexadecimal 33) back to the scan tool.

The OBD II test tool is essential for users preparing for emissions testing, as it automatically recognizes the data transfer type used by the engine control system Key features include the ability to display fault codes related to emissions, show current live values pertinent to exhaust emissions, erase fault codes, and provide an 'on-line' help facility accessible from the instrument panel.

Many features of scan tools have been available for years, catering to the growing number of computer-controlled systems in modern vehicles Technicians now expect these tools to perform diagnostics across various systems The extra pins on the 16-pin diagnostic interface enhance access to additional vehicle systems.

Fig 4.4 The Bosch KTS 300 pocket system tester

The Bosch KTS 300, illustrated in Figure 4.4, is a pocket system tester designed for OBD II applications It comes with two leads: one lead (Bosch reference 1 684 463 361) connects to exhaust emissions control units, while the other lead, featuring an adapter box as shown in Figure 4.6, links to additional control units, including ABS and transmission control systems.

Fig 4.5 The leads for the Bosch KTS 300 pocket system tester

Fig 4.6 The CARB adaptor box

The KTS 300 tester facilitates diagnostic communication once connected, guiding users through the testing process Beyond OBD II functions, it is compatible with vehicle systems equipped with an ISO 9141 diagnostic connector The diagnostic capabilities vary based on the specific vehicle and the availability of diagnostic data, and vehicle-specific connector leads are necessary for optimal performance.

Diagnostic tools that connect to the ECM 91

Fig 4.7 The flow chart that describes the fault memory processing under degree of extension 1

The KTS 300 software features two degrees of extension, with degree of extension 1 enabling users to select the fault code memory and access the 'help' menu, facilitating communication between the tester and the ECM As illustrated in Fig 4.7, users can read and clear fault codes (DTCs) as needed Navigation is straightforward: pressing the '>' key advances to the next screen menu, while the 'N' key returns to the previous step.

At a degree of extension 2, users have three options available (see Fig 4.8) Option 1 enhances the fault memory processing capacity of degree of extension 1 by adding extra items, while Options 2 and 3 offer access to screen menus that significantly improve diagnostic capabilities.

If you examine the flow chart shown in Fig 4.9, you will gain an impression of the diagnostic work that can be performed under option 1 For example, if the

Fig 4.8 The options in degree 2

Diagnostic tools that connect to the ECM 93

Fault 1 Path fault Fault type Fault code

Suppl inform.static fault/sporadic Environmental conditons

Continue: > sporadic static no no yes no yes

Loose contacts in wiring harness or plug CU

Check plug, wiring harness and components

Look for faults toward components

Manipulation plug toward before last fault

Fault memory has been cleared.

Diagnostic tools that connect to ECM

The control computer ECM, as discussed in Chapter 3, has significant self-diagnostic capabilities, with stored DTCs serving as a crucial diagnostic resource Its continuous monitoring of inputs and outputs allows data to be shared with other computers using the same protocols This feature enables microprocessor-based diagnostic tools to analyze system behavior in real-time and capture data for in-depth examination For effective communication between the test equipment and the ECM, a compatible serial diagnostic interface is essential, as illustrated in Fig 2.5, which outlines the basic principle of a serial data connector.

The adoption of the USA OBD II and California Air Resources Board (CARB) standards is increasing, but the ISO 9141 standard remains prevalent in UK and European systems ISO 9141 allows technicians to connect a scan tool to the diagnostic plug, using compatible software, typically on a smart card, to access fault codes and other essential data.

2000 machine, as shown in Fig 4.1, is an example of diagnostic equipment that can be used for a range of diagnostic work.

The Laser 2000 diagnostic tool utilizes the on-board diagnostic capabilities of vehicle ECUs, which vary significantly among manufacturers It enables various functions, including reading fault codes and their explanations, monitoring live data during vehicle operation with simultaneous display of multiple parameters for comparative analysis, and storing up to four sets of data along with their timestamps Additionally, its snapshot mode allows for the recording of data before and after an intermittent fault during road tests, facilitating the examination of abnormalities on-screen Furthermore, the Laser 2000 can activate injectors and other components for independent testing, showcasing its versatility in vehicle diagnostics.

Diagnostic tools that connect to the ECM 87

4.1.1 ACCESSING DIAGNOSTIC DATA WHEN THERE IS NO SERIAL PORT

In the UK, vehicles typically have an average lifespan of around 10 years, leading vehicle technicians to encounter various computer-controlled automotive systems, some lacking a serial diagnostic port To address this, the Lucas Laser machine can be modified for use with these systems by incorporating the Lucas Laser 1500, a data acquisition unit that connects between the Engine Control Module (ECM) and the main harness connector Once properly secured, the Laser 2000 machine can then be linked to the Laser 1500, enabling efficient diagnostics and data retrieval.

The Laser 1500, equipped with a computer-controlled system, can undergo a variety of tests similar to those performed on systems with a serial port To facilitate this, specific adapter cables and overlays are necessary, enabling the Laser 1500 to be compatible with multiple systems, as illustrated in Figure 4.2.

4.1.2 OBD II TYPE DIAGNOSTIC EQUIPMENT

The OBD II diagnostic system has been in use for an extended period, with its legislation highlighting the importance of standardization in accessing vehicle diagnostic data and supporting documentation Consequently, certain diagnostic techniques may also be applicable to non-OBD II systems.

Firstly the principal features that relate to OBD II are outlined This is followed by a description of the equipment and its diagnostic functions The principal features are as follows.

1 A standard 16-pin SAE J 1962 diagnostics plug-in point, described in Chapter 3.

2 The diagnostic plug should be accessible from the driving seat and the preferred location is as shown in Fig 4.3.

Fig 4.3 The preferred location of the SAE J 1962 diagnostic interface

3 The communication between the scan tool and the ECM takes place according to one of a small number of protocols.

To initiate diagnostic communication, the diagnostics equipment sends a hexadecimal 33 signal to the ECM using a scan tool, operating at a transmission speed of 5 baud, or 5 binary bits per second.

Diagnostic tools that connect to the ECM 89

5 The ECM then sends a ‘header label’ to the scan tool in response to the intialization prompt This header label consists of information about the baud rate and two keywords.

To verify the proper setup of communication, the scan tool reverses the second keyword and transmits it back to the ECM In binary language, this inversion involves switching 0s to 1s and vice versa.

7 The ECM sends the inverted memory address (hexadecimal 33) back to the scan tool.

The OBD II test tool is designed for user-friendly operation, allowing users to prepare for tests effortlessly as the process is automated through the scan tool's control buttons Key features of the OBD II tool include its ability to automatically identify the data transfer type utilized by the engine control system, display fault codes associated with emissions, present current live values related to exhaust emissions, erase fault codes, and provide an on-line help facility accessible from the instrument panel.

Many readers familiar with scan tools will note that numerous features have existed for years With modern vehicles often having multiple ECM-controlled systems, technicians anticipate that scan tools can diagnose various systems effectively The extra pins on the 16-pin diagnostic interface enable access to additional vehicle systems.

Fig 4.4 The Bosch KTS 300 pocket system tester

The Bosch KTS 300, illustrated in Figure 4.4, is a compact OBD II system tester that comes with two essential leads for diagnostic purposes One lead (Bosch reference 1 684 463 361) connects to control units associated with exhaust emissions, while the second lead, featuring an adapter box as depicted in Figure 4.6, links to additional control units, including ABS and transmission control systems.

Fig 4.5 The leads for the Bosch KTS 300 pocket system tester

Fig 4.6 The CARB adaptor box

When connected, the KTS 300 diagnostic tester facilitates a guided test procedure, allowing users to perform OBD II functions and assess vehicle systems equipped with an ISO 9141 diagnostic connector The diagnostics available depend on the specific vehicle and the accessibility of diagnostic data, necessitating vehicle-specific connector leads for optimal performance.

Diagnostic tools that connect to the ECM 91

Fig 4.7 The flow chart that describes the fault memory processing under degree of extension 1

The KTS 300 software features two degrees of extension, with degree of extension 1 allowing users to select the fault code memory and access the 'help' menu, facilitating communication between the tester and the ECM As illustrated in Fig 4.7, users can read and clear fault codes (DTCs) as needed Navigation is intuitive, with the '>' key advancing to the next screen menu and the 'N' key returning to the previous step.

With a degree of extension set to 2, users can choose from three available options Option 1 offers fault memory processing capabilities similar to degree of extension 1, along with additional features Meanwhile, Options 2 and 3 grant access to screen menus that enhance diagnostic capabilities significantly.

If you examine the flow chart shown in Fig 4.9, you will gain an impression of the diagnostic work that can be performed under option 1 For example, if the

Fig 4.8 The options in degree 2

Diagnostic tools that connect to the ECM 93

Fault 1 Path fault Fault type Fault code

Suppl inform.static fault/sporadic Environmental conditons

Continue: > sporadic static no no yes no yes

Loose contacts in wiring harness or plug CU

Check plug, wiring harness and components

Look for faults toward components

Manipulation plug toward before last fault

Fault memory has been cleared.

In the flow chart for option 1, if a sporadic (intermittent) fault is identified, users can 'wiggle' the connectors to check for loose connections If loose connections are found, pressing the ‘>’ key will guide the user along the dotted line path to point A, continuing through the subsequent steps outlined in the flow chart.

Option 2 permits the KTS tester to perform a range of actuator tests.

Option 3 permits actual component values to be read from the ECM, e.g duty cycle, injection time etc., and compare them with values that are stored in the KTS 300 software.

The breakout box is a diagnostic aid that is normally connected to the main ECM harness connector as shown in Fig 4.10.

VEHICLE SPECIFIC ADAPTOR LEAD AND CONNECTORS

The digital multimeter

Section 3.3 highlights the limitations of fault codes and emphasizes the additional effort needed to identify defect causes Utilizing a digital multimeter is essential in this diagnostic process, as it is particularly suited for electronic systems due to its high impedance, which prevents loading on electronic devices.

The Fluke 78, illustrated in Fig 4.11, is a specialized digital multimeter designed specifically for automotive systems Its applications in automotive diagnostics and maintenance will be explored in subsequent chapters.

These multimeters come with various test leads and adaptors, as illustrated in Fig 4.12 It's essential to ensure secure connections for optimal electrical contact Additionally, test leads should be properly supported to prevent them from disconnecting during testing or becoming entangled with moving or hot components.

Fig 4.12 The Fluke test leads and connectors

Portable flat screen oscilloscopes

Cathode ray oscilloscopes have been essential tools for diagnostic work in workshops for many years However, advancements in liquid crystal display (LCD) and thin film transistor (TFT) technology have enabled the creation of compact, portable oscilloscopes These modern devices are now offered by various suppliers at affordable prices.

Diagnostic tool and oscilloscope combined 97 cost For electronic system diagnosis they have considerable value because they are versatile and can measure sensor and other components’ performance very accurately.

Fig 4.13(a) The Bosch PMS 100 portable oscilloscope

The scope patterns presented in Chapters 4 and 5 primarily originate from the Bosch PMS 100 oscilloscope, illustrated in Fig 4.13(a) Fig 4.13(b) displays various screen menus that highlight the testing capabilities of this instrument Additionally, other oscilloscopes, including the Lucas YWB 220 and the Crypton CPT 50, are anticipated to offer comparable testing functionalities.

Diagnostic tool and oscilloscope combined

The Bosch KTS 500 represents a significant advancement in automotive diagnostics, providing technicians with enhanced diagnostic capabilities This tool connects seamlessly to the diagnostic port, enabling efficient and accurate vehicle assessments.

Fig 4.13(b) An overview of available test functions from the MENU key of the Bosch

This instrument features on-screen fault-finding aids, including troubleshooting and repair guides, as well as circuit diagrams With its large memory capacity, it can display and store live data effectively.

‘captured’ during a road test and display it on screen, or print it out for analysis in the workshop The chart in Fig 4.15 shows how vehicle identification followed

The Bosch KTS 500 control unit diagnosis tester allows for fault code read-out, which can be complemented by actual value readings Further details on utilizing data from this machine are explored in Chapter 7.

Pressure gauges

VACUUM PUMPS AND GAUGES

A vacuum pump and gauge, like the one illustrated in Fig 4.17, serve multiple functions, including evaluating the performance of MAP sensors, EGR valves, and various vacuum-operated devices.

Fig 4.15 Part of the procedure for use of the Bosch KTS 500 instrument

A vacuum pump is utilized to simulate manifold vacuum for testing the performance of a manifold absolute pressure sensor or an exhaust gas recirculation valve, as illustrated in Fig 4.18.

When the vacuum gauge and pump are used to test a MAP sensor, the vacuum pipe from the inlet manifold is removed and the pump and gauge are connected to

Fig 4.16 Pressure gauge and fuel gallery pressure check

Fig 4.17 The Lucas vacuum gauge and its adaptors

Fig 4.18 Using a vacuum pump to replace manifold vacuum in a test on an EGR valve

To test a manifold absolute pressure sensor, first ensure the vacuum connection is secure Next, connect a meter to the sensor's signal wire while supplying electrical energy, making sure the engine is not running Figure 4.19 illustrates this testing setup.

Starting with zero vacuum, i.e., at atmospheric pressure, the frequency reading should be written down The vacuum should then be increased in steps of 25 mm

Diagnostic data sources indicate that mercury vacuum gauge readings and frequency outputs are recorded at each step until a maximum vacuum of around 750 mm of mercury is achieved These readings can be compared to those of the sensor being tested, with the frequency typically ranging from 70 to 150 Hz, where lower frequencies correspond to maximum vacuum levels.

Calibrating test instruments

To ensure accuracy, it is essential to regularly calibrate measuring instruments, as they can lose precision over time Periodic checks against reliable reference readings, known as ‘calibration,’ help maintain the integrity of instrument measurements Regular calibration is a good practice for all measuring devices For example, Figure 4.20 illustrates the calibration procedure for the test leads of the Bosch PMS.

The supplier of any test instrument will normally provide a calibration service and often this service is included in the equipment service engineer’s routine.

Location charts and wiring diagrams

A location chart, like the one depicted in Fig 4.21, illustrates the placement of individual sensors, actuators, and other components on a vehicle These charts are valuable tools for conducting visual inspections and for identifying device locations to verify connections or perform back probing for testing purposes.

Circuit diagrams, also known as wiring diagrams, are crucial for verifying electrical circuits Modern diagnostic tools often incorporate location charts and circuit diagrams within their software, providing convenient on-screen access for users.

Sources of diagnostic data

Manufacturers and suppliers of diagnostic equipment typically offer services that guarantee users access to crucial diagnostic data for various vehicles Many of these services include subscription options for timely updates, while most companies also feature a hotline service to assist with diagnostic issues.

A number of publishing companies also produce books of data and fault codes and these are readily available from companies such as those listed in theAppendix.

Fig 4.20 Calibrating the test leads on the Bosch PMS 100

Exhaust gas emissions and emission system testing 105

Exhaust gas emissions and emission

PETROL ENGINE EMISSIONS 4.21

Petrol, a hydrocarbon fuel made up of about 85% carbon and 15% hydrogen by mass, requires a precise amount of oxygen for efficient combustion to power engines The necessary oxygen for this process is sourced from atmospheric air, which comprises roughly 23% oxygen and 77% nitrogen by mass Understanding the chemical equations that dictate fuel combustion is essential for optimizing engine performance.

For correct (stoichiometric) combustion this can be interpreted as: 1 kg of carbon requires 2.67 kg of oxygen and produces 3.67 kg of carbon dioxide.

Exhaust gas emissions and emission system testing 107

In this case stoichiometric combustion is achieved when 1 kg of hydrogen is supplied with 8 kg of oxygen to produce 9 kg of H2O (steam).

The primary products of combustion in exhaust gas are carbon dioxide (CO2) and nitrogen (N2), with steam being converted back to water in the atmosphere and not included in the analysis Therefore, the two main constituents of exhaust gas are CO2 and nitrogen.

Arising from the composition of the fuel and the atmospheric air that provides the oxygen, correct combustion requires approximately 14.7 kg of air for each

The air-to-fuel ratio is determined by dividing the mass of air by the mass of fuel, with a standard ratio of 14.7:1 referred to as lambdaD1 When the fuel mixture is rich, meaning there is excess fuel, the lambda value falls below 1, while a lean mixture, characterized by insufficient fuel, results in a lambda value greater than 1 This lambda value is frequently mentioned in literature related to catalytic converters and engine management systems.

During operation, petrol engines experience varying air-fuel ratios around the ideal 14.7:1, leading to the presence of gases like carbon monoxide (CO) and unburnt hydrocarbons (HC) in the exhaust These emissions, alongside carbon dioxide (CO2) and nitrogen (N2), increase under different operating conditions High temperatures in the engine cylinder cause nitrogen to react with oxygen, producing nitrogen oxides (NOx), particularly at high engine loads To mitigate NOx emissions, three-way catalysts and techniques such as exhaust gas recirculation and secondary air injection are employed.

In the UK, a vehicle is tested annually for exhaust emissions and enforcement authority officials can stop a vehicle at any time to carry out spot checks.

An exhaust gas analyser, commonly produced by garage equipment manufacturers, is essential for testing vehicle emissions These four-gas analysers detect levels of CO2, hydrocarbons (HC), carbon monoxide (CO), and oxygen (O2) in exhaust samples Additionally, they provide the air-fuel ratio, or lambda, which is crucial for diagnosing emissions-related issues, including faulty oxygen sensor signals, catalyst malfunctions, blocked air filters, and defective fuel injectors.

Department of Transport test stations rely on manufacturers' figures to ensure compliance with varying standards, making precise data essential for testing If a system exceeds limits at idle speed, most systems feature an adjustment mechanism to correct the mixture and bring the CO% reading back within acceptable limits, as illustrated in Figure 4.23 for an early model Rover car.

In addition to the diagnostic work that can be performed with the aid of the exhaust gas analyser, the self-diagnostic capability of the ECM also provides

Fig 4.23 The idle air adjustment to correct CO% valuable information through the fault codes as it constantly monitors the perfor- mance of the engine management system.

DIESEL ENGINE EMISSIONS

Diesel fuel, while derived from the same crude oil as petrol, exhibits distinct properties such as lower volatility and higher viscosity Although its composition is similar in carbon and hydrogen content, the unique mixing of air and fuel in the combustion chamber, coupled with high pressures for spontaneous combustion, creates varying conditions that lead to significant emissions issues Consequently, smoke (soot) and nitrogen oxides (NOx) are the primary concerns associated with diesel engine emissions.

Exhaust gas recirculation and precise fuelling control effectively reduce NOx emissions Compliance testing involves using an analyser to measure smoke opacity, represented by the symbol K Initially, the UK tests set two maximum opacity levels: K D3.2 for naturally aspirated engines and K D3.7 for turbocharged engines.

Fig 4.24 A d iesel fault tracing c hart (Lucas CAV)

In the early to mid-1990s, a survey by the Institute of Road Transport Engineers revealed that 99% of naturally aspirated engines and 96% of turbocharged engines met emission limits However, by March 2000, these figures had changed, with allowable limits set at 2.5 for naturally aspirated and 3.0 for turbocharged engines Additionally, smoke test meters, similar to exhaust gas analyzers for petrol engines, serve as valuable diagnostic tools, as illustrated in Fig 4.24, which identifies engine components likely to cause excessive smoke.

Smoke meters are essential tools produced by most garage equipment manufacturers, similar to exhaust gas analyzers These devices are crucial for garages that are authorized to conduct vehicle testing, ensuring compliance with emissions standards.

The Garage Equipment Association of Daventry, Northamptonshire is the trade organization for garage equipment manufacturers and suppliers in the UK.

Review questions

1 For diesel engine emissions testing in UK MOT test stations it is necessary: (a) to use a chassis dynamometer?

(b) to use an approved smoke meter?

(c) to take a sample of exhaust products and do a chemical analysis?

(d) to hold a piece of white paper over the exhaust outlet?

2 The ‘flight recorder’ function on some diagnostic equipment:

(a) permits the capture of live data from just before an intermittent fault happens and for a period afterwards?

(b) can only be used on very expensive vehicles?

(c) keeps a permanent record of the vehicle’s service history?

(d) can only be used in the workshop?

3 A digital multimeter is preferred for work on computer controlled systems because:

(a) it has a low impedance (internal resistance)?

(c) they are cheaper than moving coil instruments?

(d) the test leads make it easier to backprobe at a sensor?

4 An oscilloscope is useful for petrol injector tests because:

(a) the amount of fuel injected is shown on the screen?

(b) the shape of the injector pulse can be seen and the duty cycle is calculated? (c) the screen display shows up misfiring of the spark plug?

5 A vacuum pump and gauge permit:

(a) devices such as a manifold absolute pressure sensor (MAP) to be tested without the engine running?

(b) idle control valves to be reset to the CO% emissions level?

(c) the evaporative purge control solenoid to be tested?

(d) the wastegate valve on turbocharged engines to be tested?

6 All test instruments should be calibrated at regular intervals:

(a) to stop them wearing out?

(b) to keep the battery charged?

(c) to ensure that they are making accurate measurements?

(d) because regulations are constantly changing?

7 Fuel gallery pressure in a petrol injection system:

(a) does not need checking because it is controlled by a pressure regulator? (b) can be checked by means of a pressure gauge?

(d) is set at approximately 200 bar?

8 Backprobing of sensor connections should only be done with great care because:

(a) it may upset the readings?

(b) damage to the insulation may allow moisture to enter and cause corrosion? (c) closed-loop oxygen sensors need to be disconnected in order to get a correct reading?

Vehicle sensors are crucial components that supply the necessary inputs for the Engine Control Module (ECM) to ensure proper system functionality These sensors typically transmit voltage signals, which the computer's processor interprets as codes If the voltage readings are inaccurate, the processor may classify them as invalid inputs, leading to fault recording.

When a controller receives an incorrect sensor signal, it often indicates an issue with the sensor or its connecting circuit, rather than the sensor itself being faulty This typically results in a fault code indicating a 'sensor fault,' which signifies that the signal reaching the controller was defective It's essential to understand how sensors operate, their expected performance, and how to assess their functionality to ensure effective diagnosis and repair.

Electromagnetic sensors

HALL EFFECT SENSORS

Figure 5.6 shows the principle of a Hall type sensor The Hall element is a small section of semiconductor material such as silicon When connected as shown in

Zero volts, because magnetism is removed from the Hall element

Voltage due to magnetism across the Hall element S

Metal plate diverts the magnetism away from the Hall element

Fig 5.6 The principle of a Hall type sensor

The Hall effect sensor operates by allowing current to flow through the semiconductor Hall element when connected to a battery circuit, while no current flows in the perpendicular circuit, indicated by a zero reading on the voltmeter When a magnetic field is applied, current begins to flow in the second circuit; however, blocking the magnetic effect stops the current This on-and-off switching of current in circuit 2 can be achieved by shielding the Hall element from the magnetic field By mounting a metal plate on a rotating shaft, the Hall current can be toggled at various frequencies Notably, the output power of Hall effect sensors remains consistent across different speeds, making them ideal for applications such as engine speed monitoring, ABS wheel sensors, and camshaft identification for ignition and fuel management.

Hall effect sensors generate a low voltage output, necessitating the integration of amplifying and pulse-shaping circuits Consequently, these sensors produce a digital signal represented as a rectangular waveform, as illustrated in Fig 5.7.

Fig 5.7 A Hall sensor output signal

Optical sensors

When light interacts with semiconductor materials, it transfers energy that alters the semiconductor's electrical properties This phenomenon is utilized in optoelectronic devices, functioning as either photodiodes or phototransistors.

Figure 5.8 shows a vehicle speed sensor The photocoupler consists of an infrared beam that is directed onto a photodiode The infrared beam is interrupted

Combustion knock sensors utilize a light-shielding rotor, or chopper, driven by the speedometer This mechanism activates the light-sensing element, turning it on and off at a frequency that corresponds to the vehicle's speed.

Optical sensors are versatile devices applicable in various fields, including vehicle speed sensing, ignition systems, and steering systems These sensors operate using a power source and generate a distinct voltage pattern characteristic of their signals, as illustrated in Fig 5.9.

Fig 5.9 Signal from an optoelectronic (light sensitive) sensor

Combustion knock sensors

A knock sensor in engine control systems employs the piezoelectric generator effect, generating a small electric charge when compressed and relaxed Effective materials for this application include quartz and ceramics like PZT, a combination of platinum, zirconium, and titanium Positioned on the engine block near cylinder number 3, the knock sensor optimally detects vibrations caused by combustion knock in any of the four cylinders.

Combustion knock typically occurs near the top dead center (TDC) in engine cylinders The engine control module (ECM) utilizes stored data to adjust ignition timing based on detected knock signals, effectively eliminating the knock Once the knock subsides, the ECM gradually advances the ignition timing back to its standard setting The process of converting vibrations from knock into electrical signals is depicted in Fig 5.11.

The sensor is meticulously engineered, with the center bolt precisely torqued to pre-tension the piezoelectric crystal Additionally, the steel washer that constitutes the seismic mass is manufactured to exact dimensions This level of precision is crucial when detecting combustion knock.

Fig 5.10 The knock sensor on the engine

The piezoelectric combustion knock sensor operates by transmitting mechanical vibrations through a seismic mass to a piezoelectric crystal This crystal responds to the vibrations by 'squeezing' and relaxing, generating a small electrical signal that oscillates at the same frequency as the knock sensor The electrical signal is then conducted away from the crystal via wires securely attached to appropriate points on the crystal.

The precise tuning of the sensor is essential for accurately differentiating between combustion knock and other engine-related noises This differentiation is possible because combustion knock generates vibrations that occur within a specific frequency range.

Variable resistance type sensors

When an engine is idling, poor exhaust gas scavenging in the cylinders leads to the dilution of the incoming mixture The Engine Control Unit (ECU) must detect the throttle's idling position to adjust the air-fuel ratio for smooth engine operation Conversely, at full throttle, the mixture requires enrichment, necessitating a signal to indicate the throttle is fully open These functions are managed by the throttle position switch, which operates on the principle of a potential divider.

Fig 5.12 The principle of the throttle position sensor

The sensor generates a voltage that corresponds to the throttle position, which is then transmitted to the ECU This voltage signal, along with other inputs, enables the ECU to accurately determine the appropriate fuel delivery for specific operating conditions.

There are two distinct types of throttle position sensors, each differing significantly in their design and functionality It is crucial to identify the specific type used in any given application, as testing procedures applicable to one type may not be suitable for the other Detailed illustrations of the throttle position switch can be found in Figures 5.13 and 5.14.

Fig 5.13 Lucas type throttle position switch

Fig 5.14 Inside the throttle switch (Lucas)

Throttle position sensors are primarily electrical components that can be tested without extensive electrical or electronic knowledge Understanding the electrical signals they generate is key to effectively assessing their performance.

Variable resistance type sensors are essential for the electronic control module (ECM) to function correctly under specific conditions The throttle switch generates 'step' voltage changes at both idling and full throttle positions, enabling the ECM to accurately identify these critical throttle states In contrast, the potentiometer-type throttle position sensor provides a continuous voltage increase from idling to full throttle Consequently, it is crucial to ensure that measurements taken during testing are precise and accurately reflect the throttle butterfly's angular position, as well as the specific sensor type being evaluated For reference, Figure 5.15 illustrates the throttle position sensor utilized in the Toyota 3S-GTE engine.

The computer supplies a constant voltage of 5 V (V cc), with terminal E2 grounded through the computer Additionally, the voltages IDL and V TA correspond to the idling and throttle operating angles, respectively Figure 5.16 illustrates the relationship between the voltages at terminals IDL and V TA and the position of the throttle butterfly.

Fig 5.16 Indication of throttle sensor voltages (Toyota)

The graph presents approximate figures, emphasizing the need for specific vehicle details before conducting meaningful checks It's important to note that, like many sensors, this one can be tested using basic electrical knowledge and readily available tools, such as a voltmeter or oscilloscope Detailed testing procedures are outlined in Chapter 7.

Temperature sensors

A thermistor is a widely used temperature-sensing device that operates on the principle of a negative temperature coefficient, unlike most electrical conductors, which exhibit a positive temperature coefficient where resistance increases with temperature In contrast, a thermistor's resistance decreases as its temperature rises, a behavior characteristic of semiconductor materials This creates a clear relationship between temperature and resistance, allowing the current flow through the thermistor to provide an accurate measurement of temperature An example of a typical coolant temperature sensor is illustrated in Fig 5.17.

Fig 5.17 An engine coolant temperature sensor

The coolant temperature sensor plays a crucial role in monitoring engine temperature, as illustrated in Figure 5.18, which depicts the relationship between temperature and resistance By supplying the ECU with accurate temperature data, the sensor enables the ECU to adjust fuel delivery for optimal performance during cold starts and warm-up enrichment.

The information shown in Fig 5.18 may be given in tabular form as shown in Table 5.1 (these are approximate figures).

This shows the approximate resistance to be expected between the sensor terminals, for a given temperature From this it will be seen that it is possible to

Fig 5.18 Temperature vs resistance characteristics (thermistor)

Table 5.1 Temperature and corresponding resistance for a coolant sensor

80 280 1.2 test such a sensor, for correctness of operation, with the aid of a thermometer and a resistance meter (ohm-meter), provided the exact reference values are known.

Ride height control sensor

The sensor utilized in the Toyota height control system, as discussed in Chapter 1, operates on the principle of a potential divider, similar to various other vehicle sensor applications Figure 5.19 illustrates the detailed structure of this sensor.

The vertical movement of a vehicle's body in relation to its wheels is transformed into rotary motion by the sensor arm, which then influences the voltage detected at the sensor signal terminal This voltage is determined by the brush's position along the resistive track An oscilloscope trace illustrating the signal transmitted by the height sensor to the control computer is depicted in Figure 5.20.

(1), the suspension dampers are fully extended As the vehicle load is increased,the height decreases and this causes the sensor voltage to fall, as shown at (2) on

When the suspension reaches its lowest point, as shown in the voltage trace for a ride height sensor, the voltage level triggers the control computer to send a signal to the height control actuator, restoring the vehicle to its required height.

Manifold absolute pressure (MAP)

THE VARIABLE VOLTAGE MAP SENSOR

The MAP sensor, illustrated in Fig 5.21, operates on a 5 V supply from the ECU Changes in manifold pressure lead to the deflection of a small silicon diaphragm, which in turn modifies the resistance within the sensor's bridge circuit Consequently, the electrical output generated by the bridge circuit is directly proportional to the manifold pressure.

Fig 5.21 A manifold absolute pressure sensor

The pressure sensing element, illustrated in Fig 5.22, features four precisely controlled resistors diffused into silicon, as shown in Fig 5.22(a) Additionally, Fig 5.22(b) demonstrates how the vacuum cavity allows the silicon sensing diaphragm to flex in response to pressure changes in the induction manifold.

Fig 5.22 Details of the strain gauge type of MAP sensor

The sensing diaphragm's flexing causes changes in the physical sizes of resistors R1 to R4, impacting their electrical resistance In the sensor's bridge circuit, an increase in manifold pressure results in a rise in the electrical resistance of R1 and R3, while R2 and R4 experience a corresponding decrease This variation alters the voltage levels at the differential transformer's inputs, producing a sensor output voltage that is directly proportional to manifold absolute pressure An idealized graph illustrates the relationship between sensor voltage and manifold absolute pressure, indicating that the accuracy of a MAP sensor can be evaluated using standard electrical testing methods.

OTHER MAP SENSORS

Figure 5.23 gives an indication of the principle of operation of the variable- capacitance type of MAP sensor.

Fig 5.23 Principle of a capacitive-type MAP sensor

Capacitance (C) is defined by the formula C = ε₀(A/d), where ε₀ represents the permittivity in a vacuum, A is the area of the metallized plates, and d is the distance between the plates In this setup, the metallized plates are positioned on either side of an evacuated capsule, which is housed within a chamber connected to a manifold pressure system As the manifold pressure fluctuates, the distance (d) between the capacitor plates varies, leading to changes in capacitance (C) This capacitor is integrated into an electronic circuit that translates these capacitance variations into electrical signals.

The variable-inductance MAP sensor operates on the principle that the inductance of a coil changes when the position of an iron cylinder at its center is adjusted This mechanism is visually represented in Figure 5.24.

Fig 5.24 Variable inductance-type MAP Sensor

The iron cylinder's movement within the coil is influenced by the diaphragm and spring, leading to variations in manifold absolute pressure that affect the suction force on the diaphragm These changes in suction result in corresponding alterations in inductance, which are directly linked to the manifold absolute pressure The coil is integrated into an electronic circuit designed to ensure that the frequency changes in the square-wave output accurately reflect the manifold absolute pressure.

Figure 5.25 shows the approximate form of the variable frequency output of sensors of this type.

Access to accurate data and figures related to vehicle systems is crucial for effective maintenance and diagnostics This guide outlines general principles, but it's essential to note that diagnostic equipment suppliers often offer support services that supply test data for various vehicles and systems This factor should be carefully considered when deciding on the purchase of diagnostic equipment.

Exhaust gas oxygen sensors

THE VOLTAIC-TYPE EGO SENSOR

The zirconia (ZrO2) oxygen sensor functions by measuring the difference in oxygen partial pressure between atmospheric air and exhaust gas At sea level, atmospheric air contains about 21% oxygen, resulting in a partial pressure of approximately 0.2 bar In contrast, the oxygen content in exhaust gas can range from nearly zero in rich mixtures to about 10% in lean mixtures, leading to a partial pressure of oxygen in exhaust gas between near zero and roughly 0.01 bar.

High pressure oxygen in the atmosphere

Low pressure oxygen in exhaust gas

Atmospheric side Exhaust gas side mV mV Platinum electrode

Zirconia ZrO 2 electrolyte (sandwiched between platinum) Passage of ions

(Connected to atmospheric side electrode)

Voltage from sensor is used by the ECM to keep lambda = 1

Fig 5.27 The EGO sensor as a voltaic cell

The sensor element functions as a cell (battery) with platinum plates separated by a ceramic zirconia layer that serves as an electrolyte These platinum plates not only act as catalysts for oxygen but also facilitate the conduction of electricity from the sensor When oxygen interacts with the platinum, it triggers a catalytic reaction that enables the transport of oxygen ions through the electrolyte, generating an electric current that produces the sensor's e.m.f (voltage) This voltage accurately reflects the oxygen content in the exhaust gas.

The sensing element is designed in a thimble shape, maximizing the exposure of platinum to exhaust gases on one side and atmospheric air on the other A porous ceramic material covers the platinum exposed to the exhaust, allowing oxygen to reach the platinum while shielding it from harmful contaminants in the exhaust products.

Fig 5.28 Diagrammatic representation of the oxygen sensor in the exhaust pipe

The voltage produced by the Exhaust Gas Oxygen (EGO) sensor increases with the difference in oxygen levels between atmospheric air and exhaust gas A shift in the air-fuel ratio from slightly rich (14:1, lambda D 0.93) to slightly weak (16:1, lambda D 1.06) results in a significant change in the oxygen partial pressure of the exhaust, causing a notable change in EGO sensor voltage This sensitivity to oxygen levels is due to the ceramic electrolyte, zirconia, used in the sensor.

The sudden voltage change in the sensor triggers the ECM to adjust fuel levels, ensuring the air-fuel ratio remains chemically correct (lambdaD1) This adjustment causes the EGO sensor output to fluctuate, maintaining smooth engine operation and proper exhaust catalyst function The frequency of this output is defined by the ECM's ROM program, allowing for standardized measurement of the voltaic-type EGO output with commonly available repair equipment.

The voltage waveform generated by the EGO sensor during operation, depicted in Fig 5.30, illustrates how the Engine Control Module (ECM) adjusts fuel injection by varying the fuel amount.

Fig 5.29 Change in sensor voltage as air – fuel ratio changes

The voltage waveform of an EGO sensor is designed to maintain the air-fuel ratio within specified limits, with variations in frequency corresponding to engine speed This frequency is influenced by the type of fueling system, whether single-point or multi-point injection Nonetheless, the fundamental principle remains consistent, and a properly functioning oxygen sensor will produce a similar waveform.

The performance of an oxygen sensor is influenced by its temperature, requiring it to reach approximately 250°C for optimal functioning To facilitate rapid heating from a cold start, it is standard to incorporate a resistive-type heating element in the sensor design.

Most oxygen sensors feature four wires: one signal wire and one ground for the sensor element, along with a power wire and a ground for the heating element This design is referred to as a heated exhaust gas oxygen sensor (HEGO).

Fig 5.31 A resistive-type heating element

Fig 5.32 A heated exhaust gas oxygen sensor

The EGO sensor is integral to a feedback system and must be tested while the engine is warmed up and running; if disconnected, it will not function properly When operating correctly, the EGO sensor output ranges from approximately 200 mV to 800 mV, with a specific voltage waveform shape illustrated in Fig 5.30.

THE RESISTIVE-TYPE EGO SENSOR

The zirconia-type EGO sensor operates slowly, whereas the titanium oxide (titania)-type EGO sensor offers a quicker response time, making it more effective for engine emission control.

Steel protection tube Lead wires

Fig 5.33 The titanium dioxide (titania) type EGO sensor

The titania sensor detects variations in the partial pressure of oxygen within exhaust gases, as changes in oxygen concentration affect the sensor's material resistance When a fixed voltage is applied from the control unit, the resulting current fluctuation through the sensing element indicates the oxygen levels in the exhaust gas.

The titania sensing element functions as a semiconductor, with its resistive properties influenced by oxygen concentration This interaction alters the sensor's resistance, allowing the sensor voltage to accurately reflect the partial pressure of oxygen in exhaust gases Unlike voltaic sensors, this type produces higher voltage levels, exhibiting low voltage for rich mixtures and high voltage for lean mixtures.

In the critical region where the air-fuel ratio is chemically balanced (lambdaD1), the sensor element exhibits a significant change in resistance, generating a waveform akin to that of the ZrO2 sensor, although with a likely higher voltage output The specific voltage produced is influenced by the voltage applied to the sensor.

ON-BOARD MONITORING OF THE

The USA's OBDII regulations and upcoming European legislation mandate that vehicle emissions systems must include a malfunction indicator lamp (MIL) to alert drivers if the catalytic converter is not operating properly.

In order to meet this requirement it is current practice to fit a second oxygen sensor downstream of the catalyst, as shown in Fig 5.34.

Exhaust catalyst Exhaust flange to engine

Fig 5.34 The downstream oxygen sensor that monitors the catalyst

In Fig 5.34, the upstream oxygen sensor (A) is crucial for providing feedback to the Engine Control Module (ECM) to regulate the air-fuel ratio effectively The second sensor (B) evaluates the catalyst's efficiency by sending a signal to the ECM, with the voltage amplitude of this signal being a critical indicator As the catalyst deteriorates or is compromised by improper fuel, the voltage amplitude from the second sensor rises, signaling a decrease in efficiency.

Air flow measurement

HOT WIRE MASS AIR FLOW SENSOR (MAF)

The 'hot wire' air flow meter, located between the throttle body and the air cleaner, features a small orifice that allows a steady flow of air for combustion to pass through Inside the sensing orifice, two wires—a compensating wire and a sensing wire—are positioned, with the compensating wire carrying a small electric current The electronic circuit measures the resistance of this wire to determine the temperature of the incoming air.

The sensing wire operates at approximately 100 °C above the temperature of the compensating wire, with this temperature regulated by adjusting the current flowing through it To counteract the cooling effect of the air entering the engine, the current in the sensing wire is increased to sustain its optimal temperature.

A 'hot-wire' air flow sensor measures air flow by varying the sensing current; as air flow increases, the current rises, and as it decreases, the current falls This change in current provides an accurate electrical representation of air flow, which is utilized by the Engine Control Module (ECM) to regulate fuel supply effectively.

Modern mass air flow sensors utilize advanced materials to integrate resistive elements into a metal foil exposed to the intake air stream Typically housed within the air intake system, these sensors operate on principles similar to those of hot wire sensors The output voltage signal from a mass flow air flow sensor, as illustrated in Figure 5.41, demonstrates variability corresponding to engine speed changes as the throttle is adjusted.

CONTINUITY OHM OPEN CLOSE MOVE

Fig 5.41 Voltage pattern from a mass flow air sensor as recorded by Bosch PMS 100 oscilloscope

The practical importance of sensor

In vehicle repair practices, particularly in garage repair shops, sensors are often replaced rather than repaired, leading to a trial-and-error approach that can be both costly and inefficient To enhance accuracy and reduce expenses, it is crucial to identify the root cause of a fault before replacing any parts.

A fault code often indicates a defective sensor signal, with most sensors linked to the ECM through a signal wire that may contain multiple connectors Any issues within the circuit connecting the sensor to the ECM are typically logged as sensor faults To verify the connecting circuit, the sensor output can be assessed at the ECM using a breakout box and subsequently checked at the sensor through back probing This diagnostic process is further explored in Chapter 7, which delves into various techniques in detail.

Review questions

1 Which sensor plays a major role in the speed density method of air flow sensing?

(d) The manifold absolute pressure sensor.

2 In OBD II systems a second exhaust gas oxygen sensor is fitted downstream of the catalyst:

(a) in case the upstream one fails?

(b) to operate the EGR system?

(c) to monitor the efficiency of the catalyst?

(d) to deal with the second bank of cylinders on a vee engine?

3 In the zirconia-type oxygen sensor the difference in oxygen levels:

(b) causes the sensor to act like a small electric cell and produce a voltage? (c) does not affect the sensor output?

(d) means that the sensor can only be used in diesel engine systems?

4 Coolant temperature sensors often have:

(b) resistance that rises with temperature?

(c) resistance that does not vary?

5 In some cases, a persistent defect in a sensor reading may cause the ECM to: (a) store a fault code and make use of a default value?

(c) make use of a reading from a standby sensor?

(d) make use of its backup voltage supply?

(c) do not rely on magnetism?

(d) are only used in ignition systems?

(a) uses a light emitter and a light sensitive pick-up?

(b) operates by switching a bulb on and off at high speed?

(c) is used to improve the driver’s range of vision?

(d) is only used with fibre optic systems?

8 A potentiometer-type throttle position sensor:

(a) indicates throttle opening by means of a variable frequency signal? (b) cuts off the air supply when stopping a diesel engine?

(c) indicates throttle opening by means of a varying voltage signal?(d) is used to change the octane rating setting of the ECM?

Actuators, including devices like fuel injectors and ignition coils, are electromechanical components controlled by the ECM's outputs Their operational efficiency can be assessed through electrical tests using multimeters and oscilloscopes Skilled technicians can diagnose issues by understanding the expected electrical behavior of functioning actuators, and identifying potential defects when test results deviate from these expectations Modern diagnostic tools often feature software that displays ideal scope patterns alongside live traces, enhancing the diagnostic process, while alternative resources like manuals or digital media can also provide reference patterns.

Actuator operation

Actuators typically function using either solenoids or electric motors Solenoid-operated actuators can be controlled through two primary methods: the duty cycle method, which involves switching the solenoid on for a specific percentage of time (such as 20% or 80%), allowing for variable pulse widths to achieve the desired outcome, and pulse width modulation (PWM), where the solenoid current is toggled on and off at varying frequencies to meet operational needs Oscilloscope patterns illustrating these methods are provided in the subsequent injector tests.

Electric motors utilized in actuators can be either stepper motors or reversible permanent magnet DC motors Stepper motors are capable of delivering precise valve movements through pulsing the current supply, with some models rotating 7.5 degrees per step, resulting in a complete motor shaft rotation requiring 48 steps.

A common form of stepper motor uses two sets of windings Current in one set of windings drives the motor shaft forward and when this is switched off and

Petrol engine fuel injectors utilize a 147 current to activate an alternate set of windings, causing the motor shaft to rotate in reverse This allows for precise control of valve positioning, as the control computer accurately determines the valve's location by counting the pulses sent to the stepper motor windings.

This article highlights commonly used actuators and emphasizes the importance of caution when testing vehicle systems Making assumptions can be dangerous, so it is crucial to either have a thorough understanding of the product or access to relevant data related to it.

Petrol engine fuel injectors

SINGLE POINT INJECTION

A single-point fuel injection system features one injector located at the throttle body, specifically on the atmospheric side of the throttle valve The fuel pressure at this injector is regulated by a fuel pressure regulator, while the volume of fuel injected is controlled by the duration the injector valve remains open In this setup, fuel is directed towards the throttle butterfly, where the air velocity aids in mixing the fuel with the incoming air.

The injector valve is engineered for minimal weight, enabling rapid opening and closing When electric current flows through the solenoid winding, it generates a magnetic field that opens the valve, while the injector valve spring ensures the valve returns to its seat when the current is turned off.

MULTI-POINT PETROL INJECTION

In multi-point injection systems, each cylinder is equipped with its own fuel injector, strategically positioned to spray fuel into the induction tract near the inlet valve Figure 6.2 illustrates the design of a typical fuel injector utilized in these systems.

Multi-point petrol injection systems utilize a fuel gallery that connects the fuel pipes of all injectors, with the fuel pressure regulated by a fuel pressure regulator The amount of fuel delivered by each injector is controlled by the duration the control computer keeps the injector open, ranging from about 1.5 ms at low engine load to approximately 10 ms at full engine load, although these values may vary.

Fig 6.1 A single point, or throttle body injector

Fig 6.2 A typical injector for a multi-point injection system

Testing of petrol injectors 149 from engine to engine; larger capacity and more powerful engines will require greater amounts of fuel than small capacity and low powered engines.

Testing of petrol injectors

PEAK AND HOLD

Figure 6.3 illustrates the current flow within a peak and hold single-point injector, which operates through two earth paths managed by the ECM, as depicted in Fig 6.4.

Fig 6.3 Electric current pattern in injector

The peak current in the injector circuit occurs when it is initially earthed through both circuits Shortly after, the ECM switches off the circuit without the resistor, integrating the resistor into the injector circuit, which reduces the current through the solenoid winding An oscilloscope connected to the ECM side of the injector reveals a current flow pattern, showing a voltage rise during the hold stage as the current decreases The injector period concludes with the rising edge that occurs when the circuit is switched off To accurately measure the injector pulse duration, one must analyze the time from the first falling edge to the second rising edge on the oscilloscope trace.

CONVENTIONAL SWITCHING TO EARTH

Heavy duty transistor switches that are controlled by the ECM (as shown in Fig 6.5) are used to complete the circuit to earth in order to operate the injectors.

In this case the oscilloscope pattern will be similar to that shown in Fig 6.6.

To regulate the current flow in the injector circuit, a series resistor may be incorporated into the earth path Additionally, certain applications feature injector solenoid windings specifically engineered with higher resistance.

The high voltage observed at point (1) in Fig 6.6 results from a surge that occurs when the current is interrupted and the magnetic field of the injector solenoid collapses This marks the moment when the ECM deactivates the transistor, halting the current flow and signifying the conclusion of the injection pulse.

Fig 6.5 Earth switching of petrol injectors

The oscilloscope trace shown in Fig 6.6 illustrates the voltage for a single pulse of the injector, indicating the duration for which fuel is delivered The actual time, measured in milliseconds, can be determined by referencing the time base scale on the oscilloscope Additionally, this trace reflects the voltage supplied to the injector, typically corresponding to the system voltage.

12 V). ž This is the point at which the ECM switches on the driver transistor, to earth the solenoid winding, and it is the point at which injection commences.

PULSE WIDTH MODULATED

Pulse modulated injectors utilize a high initial current to quickly open the injector valve, followed by the ECM toggling the earthing transistor at high frequency This method ensures the injector stays open for the necessary duration while protecting the circuit from overheating The oscilloscope trace for this injector type is illustrated in Figure 6.7.

Fig 6.7 Oscilloscope trace for a pulse width modulated injector

Referring to the Fig 6.7, please note the following.

1 Current flow pulses on and off at a frequency that holds the injector valve open.

Voltage peaks occur due to surges when the injector solenoid current is turned off, leading to a collapse of the magnetic field In certain systems, these voltage peaks may be mitigated through the implementation of surge protection measures.

3 Here the injector voltage is returned to battery voltage ready for the next injector action.

The injector's 'on-time' is indicated by a sharp rise in voltage, which occurs when the current is suddenly interrupted as high-frequency pulsing begins.

5 This is where the ECM switches on the driver transistor and starts the injection period.

6 This is the supply voltage, probably battery voltage.

These explanations of the methods of operation of petrol injectors, together with the oscilloscope traces, should give a good insight into the types of test that

Fig 6.8 The general principle of a petrol injector test (a) Testing injectors for leakage.

Testing fuel delivery per injector is crucial for evaluating injector effectiveness and aiding technicians in diagnostics An injector's primary role is to supply the right amount of fuel in a combustible state as needed by the engine Therefore, comprehensive injector testing must also consider factors like the volume of fuel delivered and the spray pattern.

FURTHER INJECTOR TESTS

Figure 6.8 illustrates two types of tests that can be conducted on a vehicle It is essential that these tests are performed only by qualified personnel who have the appropriate instructions and strictly adhere to all safety precautions.

To test for injector leakage, remove the injectors from the manifold and place them over drip trays while keeping them connected to the fuel and electrical systems Energize the injectors according to the approved procedure and conduct a thorough visual inspection for leaks If any injector shows a leakage of more than two drops of fuel per minute, it is recommended to replace that injector.

Figure 6.8(b) illustrates a setup where three injectors are disconnected, allowing for precise measurement of the fuel delivered by the single connected injector Specialized injector test benches are available to conduct these tests under optimal conditions.

In many applications, the petrol injectors can be activated by the diagnostic tester through the serial port This makes it possible to hear the injectors

During the injector testing process, if the fuel supply is active, fuel will enter the intake manifold, which can potentially damage the exhaust catalyst To mitigate this risk, it is recommended to crank the engine with the spark plugs removed to expel any unburnt fuel after completing the injector test.

Exhaust gas recirculation

TESTING THE EGR SENSOR

To prevent injury, it is advisable to conduct the test on a cold engine, which is feasible only when the EGR valve can be manually lifted from its seat The expected voltage trace from this sensor type is illustrated in Fig 6.9 To capture a voltage trace, the sensor needs to be energized, and it is essential to verify that the supply voltage to the sensor is accurate.

Fig 6.9 An impression of the voltage trace from an EGR sensor

When conducting a load test, ensure that the scope connections are secure and the test instrument is positioned safely to allow for observation without personal injury risks from the dynamometer or vehicle moving parts If the test occurs during a road test, it is crucial to have an assistant accompany the test driver for safety.

The EGR valve's vacuum control is typically managed by a solenoid, which is regulated by the Engine Control Module (ECM) For testing purposes, Figure 6.10 illustrates the oscilloscope connections, while Figure 6.11 displays a standard duty cycle trace for the EGR valve.

The ECM adjusts the duty cycle to control the EGR valve's operation, allowing for the precise transfer of varying amounts of exhaust gas from the exhaust system to the intake system.

Petrol engine idle speed control

STEPPER MOTOR-OPERATED VALVE

Figure 6.12 shows a simplified arrangement of the extra air (air by-pass) valve that is built into the throttle body of some petrol injection systems.

The ECU controls the stepper motor's air valve by pulsing the transistor bases in a precise sequence, ensuring the appropriate air supply for various conditions Additionally, sensor signals allow the ECU to deliver the correct fuel amount, maintaining smooth engine operation As depicted in Figure 6.13, the stepper motor is connected to the ECU through a typical multi-pin connection, which enables easy checking of the motor's functionality.

Fig 6.13 The stepper motor and extra air valve (Lucas)

The voltage trace shown in Figure 6.14 illustrates the results obtained from testing a stepper motor using a diagnostic tool connected to the ECM's serial communication port An oscilloscope, such as the PMS 100, is effective for monitoring the pulses transmitted to the motor from the ECM, providing valuable insights into the motor's performance during testing.

Petrol engine idle speed control 159

Fig 6.15 A solenoid operated idle speed control valve

Fig 6.16 Checking an idle speed air valve

SOLENOID-OPERATED VALVE

This type of valve regulates the amount of air that by-passes the throttle valve through the medium of a solenoid-operated valve of the type shown in Fig 6.15.

In its rest position, the valve is securely closed by a spring, while the solenoid's armature is retracted within the solenoid coil When activated, the energized solenoid opens the valve, allowing air to flow into the induction system The amount of air intake is regulated by duty cycle pulses from the ECM.

The portable oscilloscope, as depicted in Figure 6.16, is utilized to assess the functionality of a solenoid-operated idle speed control valve Figure 6.17 illustrates the expected waveform pattern generated as the Engine Control Module (ECM) activates the solenoid.

To accurately assess valve operation, it is essential to monitor performance under three conditions: cold, warming up, and hot Different valve types generate distinct waveform shapes due to the behavior of inductive circuits The prominent sawtooth pattern observed in Fig 6.17(c) is a result of inductive reactance, common in many inductive devices This highlights the importance of having comprehensive product knowledge to make informed evaluations of the valve's condition.

Fig 6.17 Idle air bypass waveforms

Computer-controlled purging of the charcoal canister is managed by a duty cycle valve regulated by the ECM, with the solenoid's 'on pulse' duration adjusting based on varying operating conditions.

Fig 6.18 Testing the operation of the solenoid valve on a charcoal canister

Figure 6.18 shows the Fluke meter connected to the purge valve solenoid signal wire and earth The meter shows a 30.3% duty cycle.

To conduct this test using an oscilloscope, the connections should be made in the same manner as with the Fluke meter The resulting waveform will exhibit a characteristic shape akin to that observed during the solenoid-operated idle valve test It's important to note that the duration of the 'on-pulse' will fluctuate based on ambient temperature and the vehicle's operating conditions.

Ignition system

Computer-controlled engine management systems often utilize distributorless ignition systems based on the lost spark principle, featuring two secondary windings that produce high-tension sparks, as illustrated in Fig 6.19.

Each HT coil connects to sparking plugs, with one plug, such as in cylinder number 1, igniting near TDC during the compression stroke, while the plug in cylinder number 4 ignites at the end of its exhaust stroke The ignition system's primary side is activated by the control computer, resulting in differing ignition voltage polarities at the spark plugs due to the current flow direction in the coil's secondary winding Consequently, one spark plug receives current flowing into it, while the other experiences current flowing away.

ABS actuators

One of the main actuators on an anti-lock braking system is the unit known as the ‘modulator’ The modulator contains a pump driven by an electric motor and

Distributorless ignition systems utilize solenoid-operated valves, and simulating the actual working conditions of Anti-lock Braking Systems (ABS) for testing is challenging Consequently, ABS computers are typically equipped with extensive self-diagnosis capabilities For instance, Figure 6.21 illustrates the comprehensive fault analysis data accessible via the diagnostic link in a recent Lexus vehicle.

A clamping diode

In several of the oscilloscope tests on actuators, mention is made of the voltage

When a device like a relay, horn, or electric fan motor is turned off, a voltage spike can occur To prevent this spike, the circuit is equipped with a clamping diode that blocks the current This setup is crucial for protecting the device from damage The waveform resulting from testing these devices is illustrated in Figure 6.22.

Fig 6.20 The HT coil connections

Electronic unit injectors

Electronic unit injectors (EUI) are integral to the engine management systems of large diesel engines, with the operational data stored in the ECM's ROM Each injector consists of a cam-operated high-pressure pump and an electrically-operated spill valve, with one EUI assigned to each engine cylinder The spill valve is controlled by a high-speed solenoid known as a colenoid, which features a short travel distance.

Fuel flows into the injector from the cylinder head's fuel gallery, where a spring pushes the plunger upward, opening the spill valve while the injector valve remains seated.

Fig 6.21 Self-diagnosis data from an ABS computer

2 The cam rotates and the pump plunger covers the feed port The spill valve remains open and the injector valve is still on its seat.

As the cam continues to rotate, it drives the plunger toward the end of its stroke, causing the colenoid to close the spill valve This action enables high-pressure fuel to lift the injector valve from its seat, initiating the injection process.

4 The plunger has now reached the end of its stroke The colenoid has opened the spill valve and the injection process is completed.

Fig 6.22 Test result from a circuit that includes a clamping diode

The commencement and ending of injection can be varied by the computer control of the colenoid and spill valve.

Review questions

1 ABS computers have a good self-diagnosis capacity because:

(a) they work at high speed?

(b) their actual working conditions are difficult to simulate for test purposes?

Fig 6.23 The electronic unit injector (Lucas CAV)

(c) the braking system stops working if the ABS fails?

(d) the modulator is not under the control of the ECM?

2 A clamping diode is used on some solenoid-operated devices:

(b) to block the voltage spike that occurs when the magnetic field collapses? (c) to prevent the solenoid connections being reversed?

(d) to prevent overheating of the solenoid winding?

(a) is the number of times per second that the solenoid operates?

(b) refers to the ‘on time’ compared with the total time available to operate a solenoid?

(c) is only used on the evaporative purge control solenoid?

(d) is the length of time allowed for the transmission of an ECM command?

(a) has a high powered solenoid that controls the spill valve?

(b) is a single-fuel injector that is placed at the throttle body of a diesel engine and one injector serves all of the engine cylinders?

(c) is supplied with high pressure fuel from a ‘common rail’?

(d) is only suitable for small engines?

(a) uses a single throttle body injector?

(b) has two injectors for each cylinder?

(c) delivers fuel to each cylinder on each induction stroke?

(d) must operate the injectors by pulse width modulation?

6 In the ‘lost spark’ ignition system:

(a) there is a single ignition coil for each cylinder?

(b) the cycle of operations is completed in 540 Ž of crank rotation?

(c) there is one coil for each pair of cylinders?

(d) the polarity of the spark is the same at all sparking plugs?

(a) open a valve which is then closed by a spring?

(b) can open and close valves because they can be reversed?

(c) are not suitable for use with computer controlled systems?

(d) operate at very high speed?

(a) blow hot gas into the exhaust system to heat up the catalyst?

(b) control the movement of exhaust gas from the exhaust system into the intake system to help reduce NO x ?

(c) are not used on diesel engines?

(d) are used to operate exhaust brakes on heavy vehicles?

Chapter 5 provides various examples of sensor performance, illustrating how an oscilloscope can effectively capture readings from sensors during operation In Chapter 6, the focus shifts to the test results obtained from operating actuators, highlighting the insights gained from their performance.

This chapter delves into the fundamental principles of fault diagnosis techniques relevant to computer-controlled automotive systems It emphasizes the importance of circuit testing following fault code retrieval, covering essential concepts such as continuity, voltage drop, resistance, and current flow These principles, along with oscilloscope patterns for sensors and actuators, are applicable to nearly all vehicle systems, equipping service technicians with the necessary skills to enhance their diagnostic capabilities.

This article focuses on universally applicable factors across various systems rather than detailing individual systems Providing such specifics necessitates extensive repetition of fundamental knowledge, and the diverse variations among vehicle types and makes result in a vast amount of information needed for accurate diagnosis While some diagnostic data is readily accessible, other information is limited to authorized repairers Typically, manufacturers of diagnostic equipment offer support services that serve as valuable resources for independent garages and similar entities.

Circuit testing

The test illustrated in Fig 7.1(b) effectively checks the continuity of a circuit between the points where the meter leads are connected It is essential to ensure that the circuit is powered off, with the multimeter's battery providing the necessary electrical supply for the test Some multimeters feature a buzzer that alerts the user when the circuit is complete, while others display results on the ohm-meter scale.

Fig 7.1 Some uses of a digital multimeter

An ohm-meter indicates zero resistance in a complete circuit and infinite resistance in an open circuit, making it a valuable tool for identifying wire endpoints Additionally, it can measure the resistance of high-tension leads and other components where resistance values are crucial.

Voltage drops in a circuit can result from factors like dirty or corroded connections and poorly constructed earthing points, leading to unpredictable outcomes When current passes through a resistor, it generates a voltage drop across it To test for voltage drops, a multimeter, as shown in Figure 7.1(a), must be used while the circuit is powered on and the device is operational.

Figure 7.1(a) also shows the position of an ammeter for measuring current flow;the meter is in series.

Checking battery voltage is an important part of diagnostic work, as is the need to check the charging system voltage These checks are shown in Fig 7.2.

In many cases, sensors are supplied with a voltage via the ECM This may be a 5 V supply and is known as the source voltage If the sensor is to function

To ensure accurate charging system voltage tests, it is crucial to measure the source voltage within specific limits Careful voltage measurement is essential, as illustrated in Figure 7.3, which depicts a backprobe test used to verify source voltage In this instance, the Bosch PMS 100 scope is utilized, yielding a reading of 5.09 V.

To ensure accurate test results, it is crucial to use high-quality leads and probes Achieving 100% effective electrical connections between the test leads and the components being tested is essential Failure to establish these connections can lead to significant time and effort wasted due to false readings.

Vehicle specific details

Experienced readers understand that the variety of computer-controlled systems in vehicles is vast, making it challenging to encompass all variations in a single resource Additionally, the rapid advancements in computing technology and electronics lead to continuous changes in the design of these systems in vehicles.

The 'six-steps' approach is increasingly utilized as new technologies are integrated into designs, necessitating frequent updates of data and information Technicians at franchised dealerships receive timely notifications about these changes, allowing for rapid updates through modern technology In contrast, technicians in general garage workshops often depend on specialized companies for the necessary data and information Companies like Robert Bosch Ltd and Lucas Aftermarket Operations provide essential updating and information backup services It is crucial for technicians to have immediate access to information specific to the system being serviced and to fully understand all procedures before beginning any work.

The ’six-steps’ approach

The six-step approach is a methodical and effective strategy for diagnostic work and problem-solving This organized framework allows for recursion, meaning that it may be necessary to revisit earlier steps as one works toward a solution By following this proven method, critical steps in fault tracing and rectification are less likely to be overlooked.

4 find the cause of the fault and remedy it;

5 rectify the fault (if different from 4);

6 test the system to verify that repair is correct.

Collecting evidence in vehicle diagnostics involves thoroughly examining all symptoms related to a fault without prematurely concluding that a specific component, such as the ECU, is the cause Understanding which components are part of the faulty system is crucial, as it requires solid foundational skills For instance, if an engine control system is not functioning correctly due to poor compression in one cylinder, identifying this issue early in the diagnostic process is essential for effective troubleshooting.

When diagnosing low compression in a cylinder, it's essential to conduct tests to identify the underlying causes, such as a burnt valve or blown head gasket The analysis will differ based on the specific system being examined, but following these critical steps is crucial to avoid lengthy and unproductive electronics testing procedures.

The procedure for diagnosing issues in an electronics system depends on the available test equipment If the system includes self-diagnostics, it may identify a defective engine coolant temperature sensor To determine whether the problem lies with the sensor itself or the wiring connecting it to the system, a solid understanding of the system's components is essential.

Find the cause of the fault and remedy it

When repairing electronic systems, replacing the faulty unit is often necessary, but it's crucial to identify and address any external issues that may have caused the failure before installing the new unit Simply replacing the unit without resolving the underlying problem may lead to further complications.

Give the system a thorough test

Testing after vehicle repairs is crucial, particularly for electronically controlled systems Intermittent faults may require extended testing, as issues can arise only under specific conditions, such as when the engine is hot or during particular driving behaviors.

Skills required for effective diagnosis

Successful vehicle technicians possess a range of key skills essential for diagnosing electronic systems These include effectively using dedicated test equipment, conducting thorough visual inspections, and interpreting wiring diagrams and instruction manuals Additionally, they must adeptly utilize multimeters and other non-dedicated tools, accurately interpret symptoms of system malfunctions, and trace faults to their root causes Safety is paramount, as technicians must avoid damaging sensitive electronic components while fitting new units and making necessary adjustments Finally, they must test both the system and the vehicle to ensure optimal performance.

An approach to fault finding 175

An approach to fault finding

Having previously explored tools, technology, skills, and methods, it's essential to focus on specific details now While the on-board computer's self-diagnosis and code storage capabilities significantly aid in fault diagnosis and repair, they are not exhaustive solutions For instance, examining an engine management system reveals numerous factors influencing engine operation.

Fig 7.4 A modern engine management system (Lexus)

At the ‘heart’ of the diagram (Fig 7.4) and the engine system itself, is the engine.

In order for this engine to operate it must have:

4 a cooling system to prevent overheating;

5 a lubrication system to deal with friction and assist with cooling;

The engine's mechanism comprises essential components such as pistons, piston rings, exhaust and inlet valves, connecting rods, bearings, the crankshaft, and a flywheel These elements work together to transform combustion energy into mechanical energy, ultimately powering the flywheel.

Modern vehicles experience failures less frequently than in the past, particularly in areas (4), (5), and (6) Most issues with automotive computer-controlled systems are predominantly linked to areas (1), (2), and (3).

Certain areas are more prone to faults, indicating a concept of probability in identifying their causes When investigating potential reasons for failures, it's clear that some causes are significantly more likely to be responsible than others These probable causes have a higher likelihood of contributing to the failure.

In the past, certain vehicles experienced frequent breakdowns due to their ignition distributors being located behind the radiator and exposed to rain During heavy rainfall, water often affected the distributor, leading to malfunctions This issue became widely recognized, allowing mechanics to quickly diagnose the problem by identifying moisture at the distributor as the likely cause Such knowledge, derived from experience and empirical evidence, illustrates the importance of understanding common vehicle issues based on observed outcomes.

Motoring organizations like the AA and RAC, along with technicians involved in vehicle recovery and repair, collect valuable evidence from their experiences This data frequently identifies prevalent failure causes, including discharged batteries, insufficient fuel, and inadequate maintenance.

Whilst urging technicians to remain aware of the value of knowledge gained by experience, we now turn to the instruments and tools aspects of computer controlled systems diagnosis.

To effectively diagnose faults, it is crucial to remember the six steps, particularly the often-overlooked step of conducting a thorough visual inspection This simple yet essential action can prevent unnecessary work during the fault-finding process By analyzing a specific system failure, such as a vehicle that is not performing optimally and has an engine check lamp indicating a malfunction, one can develop a structured methodology for fault diagnosis, as outlined in the accompanying workshop documentation and flow chart (Fig 7.5).

An approach to fault finding 177

Check at sensor with portable scope

Take necessary steps for engine cranking

Read out fault 41 code Start

Make visual inspection of suspect area

Recheck for fault code NO YES O.K?

Meter readings should show zero resistance between 5 & 1 and 22 & 2.

Digital Multi Meter (DMM) set to ohms.

Note: Take down the reading.

Check sensor air gap Check for crossed connection

Fig 7.5 Flow chart showing a diagnostic technique

Engine speed sensor signal out of limits.

Checks to find possible cause:

Circuit between ECM pin 5 and sensor pin 1.

Circuit between ECM pin 22 and sensor pin 2.

(Either of these may be open circuit, short circuit or have high resistance due to corrosion at connectors.)

Cables connected to sensor pins 1 and 2 may be cross-connected.

The air gap may be too large.

The sensor coil may or its insulation may be damaged.

The potential causes extend beyond just a 'defective sensor', as illustrated in the flow chart in Fig 7.5 This chart outlines a series of procedures and tests that can be conducted using the equipment detailed in Chapter 4.

After conducting a comprehensive visual inspection of the vehicle, it is prepared for testing by connecting the diagnostic test tool to the serial port to retrieve fault codes In this instance, fault code 41 is displayed, with its specifics provided above The subsequent flow chart outlines a series of tests to be performed based on this code.

A resistance check at the breakout box connections is a common method to assess component condition, typically yielding values between 250-600 ohms However, this may not be sufficient, as a sensor can show acceptable resistance yet fail to perform correctly under operational conditions Therefore, a dynamic test using an oscilloscope while the sensor is in operation provides a more accurate assessment This test can be conducted at both the ECM connectors and the sensor connection point in the main wiring harness, allowing for checks at each end of the circuit Discrepancies in readings between the sensor and ECM indicate potential circuit faults, such as poor connections, which can be further verified with a multimeter as outlined in the flow chart.

Emissions related testing

OXYGEN SENSOR

The pre-catalyst oxygen sensor plays a crucial role in regulating the air-fuel ratio in spark ignition engines It samples exhaust gas prior to entering the catalytic converter, providing the ECM with vital information about the air-fuel mixture This feedback system enables the ECM to adjust fuel injection, maintaining lambda levels between approximately 0.97 and 1.03.

Fig 7.6 Oxygen sensor – feedback principle

Disconnecting the oxygen sensor disrupts feedback to the ECM, which is designed to activate 'limp home' mode using substitute values to protect the catalyst from damage Additionally, both the oxygen sensor and catalyst must reach an operating temperature exceeding 300 °C for optimal performance, highlighting the need for careful and detailed electrical testing of the oxygen sensor.

When diagnosing an oxygen sensor fault code, it's essential to consider various factors that influence accurate diagnosis and effective rectification.

The fault code 51 on a vehicle indicates an issue with the oxygen sensor or its circuit If no other faults are present, performing an in situ voltage test with an oscilloscope can help identify the problem It's important to note that the ECM has logged this fault code because the sensor's value is outside the programmed limits The sensor may be functioning correctly, but a defect in the connection between the sensor output and the ECM pins could prevent the signal from reaching the ECM Therefore, checking the oxygen sensor is essential.

To analyze the oxygen sensor voltage, utilize the Bosch KTS 500 tester at the ECM diagnostic port The resulting trace, exemplified in Fig 7.7, reflects the sensor's performance at idle speed, where the frequency is notably low.

2 by backprobing at the sensor, as shown in Fig 7.8.

Fig 7.7 Voltage test at the ECM diagnostic connector using the Bosch KTS 500 tester

When the system reaches its operating temperature, the sensor and circuit readings should match If the sensor reading is accurate but the ECM reading is not, this indicates a possible defect in the circuit connecting the sensor to the ECM It is essential to inspect the cables and connectors for any damage, looseness, or corrosion Additionally, continuity testing should be performed with the system powered off to ensure proper functionality.

Fig 7.8 Voltage test at the sensor using the Bosch PMS 100 portable oscilloscope between the ends of the signal cable and also the condition of the sensor’s earth connection.

When both the sensor and the ECM show similar defective signals, it suggests a sensor defect, and analyzing the oscilloscope patterns can provide valuable insights into the underlying cause The oscilloscope trace offers significant information regarding the performance of zirconia-type oxygen sensors, with key features outlined for better understanding.

As the air-fuel ratio transitions from perfect combustion (lambda D1) to a slightly rich mixture (lambda D0.98), the sensor voltage increases sharply Conversely, when the air-fuel ratio shifts from lambda D1 to a slightly lean mixture (lambda D1.02), the sensor voltage decreases rapidly.

The ECM utilizes this feature to manage fuel injection, effectively controlling the lambda value and ensuring optimal conditions for the catalyst's operation, thereby maintaining the air-fuel ratio close to the ideal chemical balance.

Fig 7.9 The zirconia oxygen sensor voltage in the region of lambda D 1

The voltage trace for a zirconia oxygen sensor, illustrated in Fig 7.10, indicates the output characteristic associated with lambdaD1 This output trace exemplifies the typical form produced by the zirconia oxygen sensor.

Points to note are as follows.

1 The maximum voltage should be between 800 mV and 1 V.

2 The slope on the rise and fall sides of the trace becomes less steep as the sensor ages, or is damaged by use of incorrect fuel or lubricants.

3 The peak-to-peak voltages should be at least 600 mV with an average of 450 mV.

4 The minimum voltage should be approximately 200 mV.

As sensors age or become damaged, such as through contamination from leaded fuel, their performance deteriorates, leading to changes in their sensor patterns A comparison of voltage traces illustrates the differences between a functioning sensor and one that has been compromised.

Fig 7.11 Comparison between a good sensor and a sluggish one and a sluggish, or aged, one The ‘good’ sensor pattern is the continuous line and the sluggish one is the broken line.

Obtaining scope patterns is a crucial part of the diagnostic process, specifically during the evidence collection step of the six-step approach Analyzing this evidence reveals key characteristics, such as lower peak voltages and reduced frequency in sluggish performance Factors influencing sluggishness include the vehicle's age, running hours, fuel type, maintenance history, and the condition of the exhaust system, which may have damage, leaks, or obstructions.

Dual oxygen sensors for catalyst monitoring

Figure 7.12 illustrates the layout of sensors and catalysts in a system that incorporates a secondary oxygen sensor to assess catalyst performance This downstream oxygen sensor is mandated by the OBD II standard to ensure compliance and optimal function.

When the catalyst functions efficiently, the downstream oxygen sensor exhibits a smoothed control voltage, indicating optimal performance This variation in voltage patterns serves as a key method for monitoring catalyst efficiency.

Fig 7.12 Dual oxygen sensors as used on OBD II type systems

When analyzing voltage patterns from upstream and downstream oxygen sensors in the ECM, a significant difference indicates a properly functioning catalytic converter If the catalytic converter fails, the voltage readings from both sensors will be similar, which serves as a key indicator in the fault monitoring process.

The downstream oxygen sensor is less likely to age than the oxygen sensor upstream of the catalyst This permits the downstream sensor to be used as a

‘guide’ signal to allow the fuelling ECM to compensate for any ageing in the upstream sensor.

Features of oxygen sensor performance that are monitored by the ECM include: ž output voltage ž short circuits ž internal resistance

Emissions related testing 185 ž speed of change from rich to weak ž speed of change from weak to rich.

Testing the upstream and downstream oxygen sensors

KNOCK SENSORS

A properly installed knock sensor, ensuring no overtightening and secure electrical connections, is generally reliable However, if engine 'pinking' occurs, it may indicate a failure in the sensor's signal production To test the knock sensor, gently tap the cylinder block near the sensor with a small tool, and monitor the results on an oscilloscope.

Figure 7.16(a) shows the oscilloscope probe connected to the signal lead of the sensor, the type of pattern, together with a maximum voltage and frequency that

To effectively test a knock sensor, it is crucial to reference Fig 7.16 from Robert Bosch Ltd The voltage and frequency readings will vary based on the intensity of the knock, highlighting the importance of careful measurement Additionally, when tapping the engine casting for testing purposes, extreme caution is necessary to avoid any potential damage.

AIR FLOW METERS

The air flow meter plays a crucial role in engine management by supplying the ECM with essential signals, including air flow measurements for optimal fuel injection and maintaining the correct air-fuel ratio It also indicates the throttle valve's idle position and provides insights into engine load For a deeper understanding of air flow sensors, including commonly used types, refer to Chapter 5, while this section highlights practical tests to evaluate their performance.

The flap type (potentiometer) air flow sensor

In Fig 7.17 the test probe is making contact with the signal connection on the air flow sensor The time base of the oscilloscope must be set to a suitable value.

When the throttle is gradually adjusted from fully closed to fully open and then slowly released, the resulting oscilloscope trace for the potentiometer type sensor should resemble the pattern depicted in Fig 7.18.

Fig 7.17 Test connections for a MAF

Fig 7.18 Voltage pattern for the full movement of the accelerator pedal

The analysis of Fig 7.19(a) reveals that an increase in sensor voltage at point (5) indicates rising air flow into the manifold, which correlates with increased throttle opening and engine speed At section (2), maximum air flow occurs during steady load at high speed Conversely, a voltage drop at (3) signifies a decrease in air flow, reaching its minimum at (4) when the throttle valve is closed, prompting the ECM to switch to idle control In Fig 7.19(b), the pattern from a defective potentiometer air flow meter shows spikes, indicating malfunctioning segments of the potentiometer track that can lead to issues when the sensor wiper is in those positions.

Fig 7.19 Potentiometer-type air flow sensor voltage signal

Chapter 5 outlines that sensors typically operate based on resistance changes in the sensing element due to variations in airflow, with output signals being either analogue or digital It is crucial to verify the sensor type before conducting tests An oscilloscope can be connected to the sensor's signal wire, as illustrated in Figure 7.20, to monitor the output Once securely connected, the engine should be started and allowed to idle while gradually increasing the speed, observing the oscilloscope for any irregularities Lightly tapping the sensor casing with a small screwdriver can reveal poor connections through breaks or blips in the signal pattern Figure 7.21 demonstrates a typical signal pattern for a well-functioning analogue MAF sensor.

Fig 7.20 Testing an analogue air flow sensor

THROTTLE POSITION SWITCHES

The Engine Control Module (ECM) requires real-time data on the throttle valve's position to determine when the throttle is closed and when idle control needs to activate Additionally, the throttle position sensor provides valuable insights into engine load and indicates when the throttle butterfly valve is fully open Typically, this sensor is located on the throttle butterfly spindle, opposite the throttle lever.

Fig 7.21 Oscillscope voltage pattern for an analogue MAF

Fig 7.22 Testing a throttle position sensor (switch)

Figure 7.22 shows a throttle position sensor being backprobed in order to obtain a scope pattern of the voltage signal.

With the time base of the oscilloscope set to a suitable value, the ignition is switched on The scope screen should then be observed while the accelerator

The voltage trace for a potentiometer-type throttle position sensor and a switched-type throttle position sensor pedal demonstrates a gradual transition from the fully closed to fully open position and back This movement results in a characteristic pattern, as illustrated in Fig 7.23.

Figure 7.24 illustrates an analysis of the voltage trace, which closely resembles that of a flap-type air flow meter This voltage trace not only reflects the throttle position but also includes a throttle switch with contacts that generate a step signal at both the throttle-closed and fully-open positions, as depicted in Figure 7.25.

A COOLANT TEMPERATURE SENSOR

The coolant temperature sensor (CTS) functions within a voltage range of approximately 0.2 to 4.8 V, and fault codes are typically triggered only when the voltage deviates from this range Consequently, an engine can run with a malfunctioning CTS, which may mislead the ECU by reporting a cold engine temperature despite the engine being hot This can result in the engine operating on an excessively rich fuel mixture Conducting tests within the sensor's operating range can help verify its functionality and eliminate it as a potential cause of engine issues.

Fig 7.24 Analysis of voltage trace for a potentiometer-type throttle position sensor

Fig 7.25 The throttle switch type of voltage pattern

The ECM can detect voltage at the sensor terminals, allowing for sensor checks using a voltmeter or oscilloscope As illustrated in Figure 7.26, the Bosch portable oscilloscope is utilized to assess the performance of the coolant temperature sensor.

Fig 7.26 Testing the coolant temperature sensor

In this test, the voltage drop across the sensor terminals is measured with the ignition on and the engine off, resulting in a high signal voltage due to the cold sensor element Once the engine starts and warms up to its operating temperature, the sensor voltage changes, as illustrated in Fig 7.27 Evaluating the sensor's performance throughout its operating range, from cold to hot, requires a significant amount of time, necessitating an appropriate adjustment of the scope's time base.

Fig 7.27 A voltage trace from a coolant temperature sensor

MANIFOLD ABSOLUTE PRESSURE

A preliminary visual inspection is crucial, as the vacuum pipe connecting the intake manifold to the MAP sensor may be loose or damaged This issue can significantly impact performance Refer to Figure 7.28 for the oscilloscope connections used in this test.

The voltage trace from an analogue MAP sensor over approximately 3 seconds reveals key insights into engine performance Notably, it shows variations at low and high engine loads, with high voltage corresponding to low manifold vacuum As the throttle opens, the vacuum decreases, leading to an increase in voltage, while a low voltage indicates high vacuum levels.

The voltage trace for a MAP sensor, illustrated in Figure 7.30, produces a variable frequency digital signal output that ranges from approximately 50 to 110 Hz, depending on manifold vacuum levels It is important to note that the top line of the signal should closely align with the reference voltage supplied to the sensor.

Fig 7.28 Testing a manifold absolute pressure sensor

Fig 7.29 Signal voltage from an analogue MAP

The voltage pattern of a variable frequency MAP sensor should display near-vertical rise and fall lines, indicating quick response times The peak-to-peak voltage must closely align with the reference voltage, ensuring accurate readings Additionally, the lower voltage levels should be near the earth voltage level; any voltage difference exceeding 400 mV in this area warrants further investigation.

The MAP sensor may be tested with the aid of a vacuum pump, to simulate manifold vacuum, and a voltmeter as shown in Fig 7.31.

Fig 7.31 Testing a MAP sensor with the aid of a vacuum pump

To perform this test, disconnect the vacuum pipe from the manifold to the sensor, and connect the manifold end to a vacuum pump Attach the positive lead of the voltmeter to the sensor's signal output and the negative lead to a reliable ground Ensure a secure electrical connection between the sensor's signal cable and the voltmeter lead, using connectors cautiously to maintain insulation and reliability Utilizing a vacuum pump allows for precise verification of the sensor output against the measured vacuum, offering advantages over alternative testing methods.

Ignition system tests

TESTS ON DISTRIBUTORLESS

To ensure safety in the workplace, it is crucial to prioritize 'Key Skill 7: Work in a Safe Manner.' Avoiding electric shocks from ignition systems is essential, as these shocks pose significant dangers not only on their own but also due to the risk of involuntary muscle contractions, which can lead to accidental contact with moving or hot components.

The secondary voltage trace is crucial for analyzing ignition system performance, as demonstrated by the portable oscilloscope setup shown in Figure 7.32, where the inductive pick-up is clamped to the HT lead near the spark plug The oscilloscope's screen displays important data, including engine speed and burn time, which can be further examined by enlarging the trace for a single cylinder, as illustrated in Figure 7.33.

1 Firing line This represents the high voltage needed to cause the spark to bridge the plug gap.

Fig 7.32 The oscilloscope set-up for obtaining a secondary voltage trace from a DIS

Fig 7.33 Details of the HT voltage trace for a single cylinder

5 Intermediate section (any remaining energy is dissipated prior to the next spark).

6 Firing section (represents burn time).

8 Primary winding current is interrupted by transistor controlled by the ECM.

9 Primary winding current is switched on to energize the primary The dwell period is important because of the time required for the current to reach its maximum value.

A comparison of the secondary voltage traces from each cylinder should reveal broadly similar patterns; significant differences indicate potential defects For instance, a low firing voltage suggests low resistance in the high-tension (HT) cable or spark plug, possibly due to oil or carbon fouling, incorrect plug gap, low cylinder pressure, or a defective HT cable Conversely, a high voltage indicates high resistance, which may result from a loose HT lead, wide plug gap, or excessive resistance in the HT cable Key points are summarized in Table 7.1.

Table 7.1 Factors affecting firing voltage for high and low firing voltages

Factor High firing voltage Low firing voltage

Spark plug gap Wide Small

Air – fuel ratio Weak Correct

Spark plugs can be removed and inspected, while HT leads should be checked for secure fittings and their resistance measured with an ohm-meter Resistive HT leads, designed to reduce electrical interference, typically exhibit a resistance of around 15,000 to 25,000 ohms per meter.

Here, as in all cases, it is important to have to hand the information and data that relates to the system being worked on.

Diesel injection

TESTING THE INJECTION POINT

Utilizing additional facilities within the PMS 100 scope enables simultaneous acquisition of the TDC sensor signal and pressure signal This configuration is illustrated in Fig 7.36.

At idle speed, the advance period of the engine can be observed, indicated by two vertical lines in Fig 7.37(a) As the speed increases to 1700 rpm, the impact on the advance period is illustrated in Fig 7.37(b) This test is beneficial as it allows for the verification of the injection point relative to TDC, providing insight into the proper functioning of the timing control on the pump.

Sensor tests on other systems

ABS WHEEL SPEED SENSORS

Anti-lock braking system (ABS) wheel speed sensors are crucial for the system's functionality and play a vital role in traction control and stability control systems Typically, these sensors operate based on the variable reluctance principle, as illustrated in the setup for a wheel speed sensor test in Fig 7.38.

Fig 7.38 A test on an ABS wheel speed sensor

Sensor tests on other systems 205

To conduct the test, the road wheel must be rotated at an adequate speed to produce a signal, which is typically accomplished by safely jacking up the vehicle and manually rotating the wheel It is crucial to follow the vehicle manufacturer’s recommended procedures for any alternative methods of wheel rotation The sensor output should resemble the format illustrated in Fig 7.39, with both voltage and frequency varying according to the speed.

Fig 7.39 Testing an ABS wheel sensor

The main points to look for on the voltage trace are: ž a regular waveform ž any gaps in the waveform that may indicate a missing tooth or displaced reluctor ring ž low voltage.

Some ABS and traction control systems utilize Hall-type sensors, which require a power supply for proper operation Testing these sensors demands careful attention to ensure the power supply is functioning correctly The testing procedure is similar to other methods, emphasizing the importance of safely jacking up the vehicle and rotating the wheel during the process Hall-type sensors generate a frequency pattern, as illustrated in Fig 7.40.

Fig 7.40 The pattern of the signal from a Hall type ABS sensor

TESTING THE RIDE HEIGHT CONTROL

The computer-controlled suspension system employs a variable resistance-type sensor to generate a voltage signal that indicates the ride height As illustrated in Figure 7.41, a portable oscilloscope is utilized to measure this voltage.

Fig 7.41 Testing a ride height sensor

Intermittent faults 207 trace from the ride height sensor The same test can be performed by using a digital voltmeter set to a suitable range.

After confirming the electrical supply to the sensor and locating the signal cable, disconnect the sensor's movable arm from the axle or suspension unit for manual activation Once the oscilloscope or voltmeter is properly connected to the signal lead, ideally through backprobing, move the sensor arm through its entire operating range to assess its functionality.

A scope pattern resembling that in Fig 7.42 is expected If the voltage does not fluctuate with arm movement or experiences abrupt drops, it signifies a malfunction in the sensor.

Fig 7.42 Result display of a voltage test on a ride height sensor

While testing the sensor can determine its electrical functionality, issues may arise from the mechanical linkage connecting the sensor to the suspension system If the linkage is worn, damaged, or if the sensor is improperly positioned, the signal sent to the ECM may not match its programmed values, leading to potential malfunctions in the height control system Therefore, it is crucial to conduct a comprehensive visual inspection of the system early in the diagnostic process.

Intermittent faults

Modern computer-controlled systems offer self-diagnosis capabilities that greatly assist technicians in identifying occasional faults The onboard computer's processing power and memory are instrumental in pinpointing the causes of these issues Additionally, many diagnostic scan tools feature a data logger function, akin to an aircraft's flight recorder, which is often referred to as the 'flight recorder' function in automotive diagnostics.

7.10.1 FLIGHT RECORDER (DATA LOGGER) FUNCTION

The data logger functionality of test equipment enables the storage of critical data obtained through the ECM's serial data diagnostic connector, which is essential for diagnosing faults like unexpected power drops during acceleration During a road test, a driver, accompanied by an assistant to operate the test equipment for safety, drives the vehicle while the equipment is set to 'record' mode The goal is to replicate the fault condition, and when the issue arises, the control button is activated to capture data from before and after the incident This recorded data can later be analyzed on an oscilloscope or printed for further examination in the workshop, as illustrated in Figure 7.43, which showcases live data collected from a Bosch KTS 500 test on a Peugeot vehicle.

Fig 7.43 A display of live data as ‘read’ out from the diagnostic link

The signals are currently functioning correctly, but any defects may manifest in the displays shown For instance, Figure 7.44 illustrates the kind of information that could be observed in such cases.

Drops when it should raise !

Fig 7.44 How a probable fault shows up in a live data display

The vehicle is experiencing acceleration, indicated by the increased throttle opening, engine speed, and fuel injection Typically, such acceleration should coincide with a rise in air flow; however, the air flow sensor is reporting a decrease, suggesting a possible fault in the sensor itself.

Summary

As vehicle systems advance and diagnostic data storage expands, designers can incorporate more detailed diagnostics, potentially allowing for the precise identification of faults through on-board computing However, issues may still arise if the circuit connecting sensors or actuators to the computer interface fails to transmit the correct signals The ability to assess sensors and actuators directly at their terminals, along with examining the circuits linking them to the computer, is crucial and can be achieved using tools like portable oscilloscopes and digital multimeters Many garage oscilloscopes offer multiple functionalities, serving as voltmeters, ohmmeters, and frequency meters, making them essential tools for technicians involved in vehicle repair and maintenance.

The growing availability of diagnostic data and the production of fault code manuals by various publishers highlight the vital role of independent repairers in modern technology With the introduction of European on-board diagnostics, the future for these professionals appears promising I have emphasized the essential skills required for effective diagnosis, aiming to motivate trainees to commit to their studies and training to develop these crucial abilities.

Review questions

1 For voltage tests on sensor output the voltmeter is connected:

(b) between the sensor output terminal and the end of the cable that has previously been disconnected?

(c) between the signal terminal and earth?

(d) across the vehicle battery terminals?

2 It is useful to be able to test sensor performance at the sensor and at the ECM because:

(a) it provides a useful check on the wiring between the two points?

(b) it eliminates the need for intrusive testing?

(c) the two readings can be averaged to provide a value for the source voltage? (d) it is the only way to check voltage in a feedback system?

3 When an exhaust gas oxygen sensor ages:

(a) the exhaust catalyst stops working?

(b) the peak-to-peak voltage of the sensor is reduced?

(c) the peak-to-peak voltage is increased?

(d) the EGR system stops operating?

4 In a variable reluctance type crank position sensor:

(a) the air gap has no effect on sensor performance?

(b) the air gap should be checked if the sensor signal is incorrect?

(c) the sensor output voltage is not affected by speed of rotation of the crankshaft?

(d) the voltage signal can only be measured by means of a voltmeter?

5 Cylinder recognition sensors are often fitted to the camshaft:

(a) because the camshaft turns faster than the crankshaft?

(b) because they are more accessible in that position?

(c) because the camshaft rotates once for every two revolutions of the crankshaft?

(d) in order to operate single-point injection systems?

6 Modern engine management systems often adapt control programs to compen- sate for wear in components, and after fitting new units the vehicle should be driven for a suitable period to:

(a) clear the fault code memory?

(b) allow the ECM to ‘learn’ a new set of figures?

(c) allow the alternator to recharge the battery?

(d) clear unburnt fuel from the exhaust system?

(a) replaces the ECM for test purposes?

(b) permits tests to be performed at the ECM without backprobing?

(c) reads digital data because it is connected to the data bus of the ECM processor?

(d) needs only one connector to enable it to be used on any make of vehicle?

8 Sensor inputs to the ECM are:

(a) used only for generating fault codes?

(b) used to provide data that enables the ECM to know the state of variables, such as engine speed, air flow etc.?

This chapter offers supplementary insights into technologies discussed in previous sections, presenting a concise overview that equips readers with foundational knowledge This introduction serves as a stepping stone for those interested in pursuing deeper exploration in their specific fields of interest.

Partial and absolute pressures

The concept of partial pressure of oxygen is crucial in understanding exhaust gas oxygen sensors According to Dalton's law, the total pressure exerted by a mixture of gases in a confined space is equal to the sum of the individual pressures that each gas would exert if it occupied the space alone For instance, in a mixture where the total pressure is 3 bar, with nitrogen contributing 2.7 bar, the partial pressure of oxygen would be 0.3 bar This illustrates how the separate pressures of gases, such as 2.7 bar for nitrogen and 0.3 bar for oxygen, are defined as their partial pressures.

It is the partial pressure of oxygen in exhaust gas that is the variable of interest for the lambda sensor that is used in the emission control system.

Most pressure gauges are designed to display zero pressure at atmospheric conditions, effectively disregarding atmospheric pressure As a result, the readings from these gauges are referred to as "gauge pressure," as they measure pressure relative to the atmosphere To determine absolute pressure, it is essential to account for barometric pressure.

At an atmospheric pressure of 1015 mbar (1.015 bar), a recorded tyre inflation pressure of 2.1 bar indicates that the absolute pressure within the tyre is the sum of atmospheric pressure and gauge pressure, resulting in a total of 3.115 bar.

Barometers record absolute pressure and the pressures that are shown on TV weather maps are also absolute pressures.

In automotive control applications the ability to measure absolute pressure is important for at least two reasons.

1 The absolute pressure in the induction manifold, of a throttle controlled engine, is an accurate indicator of the load that the engine is operating under.

The speed density method measures air mass by utilizing the absolute pressure in the manifold, allowing the Engine Control Module (ECM) to accurately estimate the mass of air entering the engine's combustion chambers.

The characteristic gas equation, expressed as pV = mRT, illustrates the relationship between absolute pressure (p), volume of air (V), mass of air (m), the gas constant (R), and temperature (T) in the engine manifold This equation can be rearranged to m = pV/RT, providing an instantaneous calculation of the mass of air entering the engine.

The piezoelectric effect

Certain natural materials, like quartz, exhibit the piezoelectric effect, which enables them to vibrate at the frequency of an applied alternating voltage This phenomenon occurs as the voltage alters the crystal's electrical polarity, inducing mechanical strain known as the 'motor effect.' To harness this effect, a precisely sized quartz crystal is positioned between metal plates, creating a circuit that facilitates this vibrational response.

Fig 8.1 An oscillator based on the piezoelectric effect

Applying force to a crystal induces mechanical strain, alters its electrical polarity, and generates a voltage between metal plates This phenomenon, referred to as the 'generator effect,' serves as the foundation for the knock sensor utilized in numerous engine management systems.

Natural quartz contains impurities and to overcome this problem quartz is

‘grown’ in controlled conditions In addition to quartz and a few other materials,certain ceramics that are oxide alloys of platinum, zirconium and titanium (PZT),also possess piezoelectric properties.

Gives out electrical energy (generator effect)

Changed shape of crystal structure

Strains the crystal and elasticity causes vibration (motor effect)

Fig 8.2 The piezoelectric generator and motor effects

An important property of a piezoelectric material is its coupling coefficientk.

This expresses the relation between electrical and mechanical energy. k 2 Dmechanical energy output/electrical energy input or electrical energy output/mechanical energy input.

Liquid crystal displays

Liquid crystal displays (LCDs) are widely utilized in various devices, including laptops, calculators, vehicle instrument panels, and timekeeping devices Their application is expanding into diagnostic tools for automotive systems The portable oscilloscope highlighted in this book also employs an LCD, providing readers with an opportunity to understand the fundamental principles behind its operation.

Twisted nematic (TN) liquid crystals are widely utilized in LCD technology due to their rod-like molecular structure, which can be easily polarized when an electric field is applied This polarization enables the effective control of light passage, making TN crystals essential for the functionality of liquid crystal displays.

A 10µm thick layer positioned between two transparent electrodes forms a capacitor, where applying and removing electrical potential alters the polarity of rod-like molecules, thereby impacting the light transmission properties of the LCD cell.

The simple LCD cell utilizes transparent indium doped tin oxide (ITO) electrode plates, with a thin plastic layer on the inside surface During manufacturing, microscopic grooves are created in the plastic through a rubbing process, arranged perpendicularly to facilitate the smooth rotation of rod-like molecules through 90 degrees across the TN layer Additionally, the LCD cell is encased in glass, which features a polarizing filter on its surface.

LCD cells utilize TN molecules to manipulate light, allowing it to pass through at a 90-degree angle When a reflector is positioned on one side, it enhances brightness by reflecting light back through the cell Additionally, backlighting can illuminate the cell from behind However, when the electric current is activated, the rod-like molecules align with the electric field, effectively blocking the light and resulting in a dark appearance for the cell.

In order to produce a large display, suitable for a computer or oscilloscope screen, it is necessary to have a large number of cells arranged in a matrix form. Figure 8.4 shows the concept.

A small part of an LCD screen Each cell is controlled by a mosfet TFT via source and gate lines

Fig 8.4 Arrangement of some cells for the matrix of an oscilloscope screen

LCD displays create high-definition color images by combining red, blue, and green pixels Each pixel is managed by a thin film transistor (TFT), which controls the individual cells by turning them on and off through a system of addressing rows and columns.

Countering cross-talk

To prevent cross-talk, where one signal interferes with another in data transmission cables, it's often necessary to implement additional measures, such as using screened cables, especially when maintaining adequate distance between cables isn't feasible.

Twisted pair cables effectively minimize capacitive interference from nearby cables by keeping the two wires close together, which reduces susceptibility to cross-talk Additionally, this design helps counteract inductive interference, as the interference effects tend to cancel each other out along the cable's length.

A screened co-axial cable, as illustrated in Figure 8.5(b), minimizes interference by confining the interfering current to the outer surface of the screen, thereby preserving the integrity of the signal in the central conductor Proper earthing of the screen is crucial for optimal performance.

Fig 8.5 Twisted pair and screened cable

Logic devices

THE RTL NOR GATE

Figure 8.6 shows how a resistor transistor logic (RTL) gate is built up from an arrangement of resistors and a transistor There are three inputs:A,B, andC If one

An RTL NOR gate produces a low output (logic 0) when any of its inputs are high (logic 1) This output is represented as ACBCC with a bar over it, indicating the operation 'not A or B or C,' which defines the NOR function (NOT OR).

Base resistors (R b) are crucial for ensuring that the base current is sufficient to drive the transistor into saturation, resulting in a low output (logic 0) when at least one input is high (logic 1).

TRUTH TABLES

Logic circuits function based on Boolean logic, utilizing terms such as NOT, NOR, and NAND from Boolean algebra While the specifics of Boolean algebra may not be essential, understanding that the input-output behavior of logic devices is represented by a 'truth table' is crucial For instance, the truth table for the NOR gate illustrates this concept clearly.

Fig 8.7 NOR gate symbol and truth table

In the NOR truth table, when the inputsAandBare both 0 the gate output, C, is 1 The other three input combinations each give an output C=1.

TTL (transistor to transistor logic) is a widely used system in computing and control systems, where logic 0 is represented by a voltage between 0 and 0.8 V, and logic 1 by a voltage between 2.0 and 5.0 V Additionally, various commonly used logic gates and their corresponding truth tables can be found in Fig 8.8.

Fig 8.8 A table of logic gates and symbols

The basic inverter, illustrated in Figure 8.9(a), converts a logic 1 input into a logic 0 output In Figure 8.9(b), a feedback loop from the output to the input creates oscillations, causing the output to alternate between 0 and 1 The frequency of these oscillations is influenced by the inverter's propagation delay time.

THE SR (SET, RESET) FLIP-FLOP

Just as the basic building blocks of electronics, e.g transistors, diodes and resistors,can be joined together to make logic gates, so those logic gates can be used as

An inverter serves as a fundamental building block for creating various logic devices, including flip-flops A flip-flop is a memory-based switching device, which plays a crucial role in sequential switching circuits Its functionality relies on both the current input and the historical sequence of inputs, making it essential for effective circuit operation.

The flip-flop circuit depicted in Fig 8.10(a) consists of two interconnected NOR gates, where the output of the second gate is looped back to serve as an input for the first NOR gate This configuration features two inputs, S and R, and produces two outputs, Q and its complement.

Q’ It is usual to show the network ‘cross-coupled’ as in Fig 8.10(b).

The network is said to have a memory because the output is dependent on past input sequences as well as present ones If the inputs are restricted so thatSand

Rcannot be logic 1 simultaneously, the outputsQandQ 0 (notQ), as shown in the truth table, are always true.

Figure 8.11 shows an SR flip-flop in an automatic switching circuit for head lamps.

A number of flip-flops may be used to make other devices, such as registers for holding digital codes, e.g 1010 (This is a four-bit binary number that represents

Fig 8.11 Automatic headlamp circuit (Toyota)

Fig 8.12 D-type flip-flops used as 4-bit register

In Fig 8.12, the inputs D0 to D3 signify binary data represented by logic levels 0 and 1 Upon receiving a high clock pulse, the register outputs the corresponding data, maintaining it until the next clock pulse This allows the data to be transferred to outputs, enabling its use as inputs for other devices.

The fundamental silicon p–n junction serves as the building block for transistors, which are essential for constructing logic gates These logic gates form the basis for flip-flops, which in turn are utilized to create registers and various other logic circuits.

ANALOGUE TO DIGITAL CONVERSION

Analog-to-digital (A/D) conversion is essential for processing sensor signals, which are often in varying voltage form To enable the control computer to operate effectively, these analog signals must be transformed into binary codes, or digital signals This highlights the importance of understanding the design fundamentals of an A/D converter suitable for use in an ECM interface Various methods exist for converting an analog voltage into a digital code, with one example being the 'flash' converter, as illustrated in Figure 8.13.

Fig 8.13 Flash-type analogue to digital converter

The flash converter features four comparators and an encoder circuit that transforms the outputs from the comparators into binary code Each electronic comparator continuously compares two signals, with one input set as a reference voltage When the input voltage aligns with the reference voltage, the comparator outputs a logic 1 The reference voltages range from 1 V to 4 V, as detailed in Table 8.1, which illustrates the input/output performance of the converter.

The encoder contains logic devices (gates etc.) and this enables it to output the binary codes for 1 to 4 These binary codes (0s and 1s) are used by the ECM

Table 8.1 Performance of the flash converter

A/D converter Comparator Encoder input voltage outputs output range A B C D

A 4-5 V processor is utilized to trigger specific actions within the ECM, with components connected by buses (wires) that carry low current electrical pulses When a binary output command is created, it typically needs to be converted to an analogue format, necessitating a digital to analogue converter at the ECU output interface.

DIGITAL TO ANALOGUE CONVERSION

A digital to analogue converter operates by utilizing power sources of 8 V, 4 V, 2 V, and 1 V, depicted as small circles in Figure 8.14 When a binary code is input, the most significant bit (MSB) plays a crucial role in the conversion process.

8 V end and the LSB at the 1 V end, the switches are operated electronically In

Fig 8.14 Basic principle of a digital to analogue converter

OBD II 223 the diagram binary 1100 (12) is placed at the inputs This means that the two inputs of 1 will switch their respective voltages of 8 V and 4 V to the output lines,and the electronic summing circuit will add them together to give a 12 V output.

OBD II

FUEL SYSTEM LEAKAGE

The Engine Control Module (ECM) is designed to register a fault when a leak equivalent to a 1 mm diameter hole is detected in the fuel tank ventilation system, as illustrated in Figure 8.16, which outlines the fundamental operation of the leakage detection system.

Fig 8.16 The elements of a leakage detection system

The fuel evaporation system includes a normal evaporative purge control (EVAP) valve and an additional valve operated by the ECM to regulate fresh air supply to the carbon canister, along with a pressure sensor located at the petrol tank When both valves are closed, the system is sealed, allowing the pressure sensor to provide readings to the ECM Upon opening the EVAP valve while the engine is running, a vacuum is created in the fuel evaporation system, resulting in a lower pressure reading captured by the ECM The valves are then closed again for a period during which the ECM continues to monitor the system.

OBD II 225 reading from pressure sensor (9) Any significant change in pressure as recorded by the sensor (9) indicates that there is a leak in the evaporation system.

SECONDARY AIR INJECTION

The aim of secondary air injection into the exhaust system is to reduce CO and

During the warm-up phase following start-up, hydrocarbon (HC) emissions are generated, but the introduction of additional oxygen enhances the catalytic converter's oxidation process This is illustrated in Figure 8.17, which depicts a system utilized by Volvo cars.

Fig 8.17 Secondary air injection system

The solenoid valve (4) is managed by the ECM, which also controls the relay (2) supplying electrical power to the air pump (3) When the ECM activates or deactivates the secondary air system, the solenoid valve (4) regulates the manifold vacuum to the combined air and check valve (6), which in turn opens and closes to direct air to the exhaust injection port.

The pre-catalyst oxygen sensor monitors the secondary air flow, and if the flow rate falls outside the manufacturer's specified limits, a fault will be logged.

The following precis of the self-diagnostic routine for the ECM of the Volvo system gives an insight into the diagnostic power of modern systems.

1 The idling and part load fuel functions are inhibited and the EVAP valve is closed The ECM checks the signal from the oxygen sensor and if this shows an unchanging maximum value, the air pump is running continuously and the secondary air valve is leaking This will cause a fault code to be recorded for the pump and valve.

2 The secondary air valve is closed and the air pump is started The oxygen sensor signal (as determined by the ECM) should remain steady If the oxygen sensor signal (at the ECM) exceeds a certain value within 6 s, the secondary air valve is leaking and a fault code for this valve will be recorded.

3 The secondary air pump runs continuously and the secondary air valve is opened In this case the oxygen sensor signals (as assessed by the ECM) should exceed a specified limit within 6 s If this does not happen, the secondary air pump is not running or the secondary air valve is not opening This will cause the ECM to record a fault code for the secondary air pump.

FREEZE FRAMES

When the Engine Control Module (ECM) identifies conditions that trigger a diagnostic trouble code (DTC), it stores the relevant sensor readings and vehicle operating conditions in its memory This stored data is presented in a format called a "freeze frame," which can be accessed using a diagnostic scan tool for effective troubleshooting It's important to note that freeze frames may be overwritten by newer, higher-priority diagnostic trouble codes within the same system.

STANDARDIZED FAULT CODES

Independent garages face challenges in repairing vehicles with computer-controlled systems due to limited access to diagnostic trouble codes (DTCs) While companies listed in the Appendix provide extensive DTC volumes for various vehicle types, inconsistencies in the codes exist Despite these discrepancies, the codes effectively identify faults in components that are often identical or very similar across multiple vehicles.

OBD II overcomes this problem because it stipulates the use of standardized fault codes It achieves this standardization by making use of SAE standards such asSAE J 1930 and SAE J 2012 The SAE J 1930 standard provides a system for naming the component parts of a computer controlled automotive system and SAE J 2012 details the DTC descriptions It is understood that the European OBD standards for DTCs are likely to be very similar to the SAE ones and a sample of these is given in the Appendix.

Computer performance (MIPS)

In previous chapters, I discussed the concepts of performance, power, and capacity in computers, which are often debated topics A commonly used metric for measuring computer performance is MIPS (millions of instructions per second), indicating the speed at which a processor executes instructions However, since different instructions require varying amounts of time to complete, MIPS serves only as a general guideline for performance For a more accurate comparison of computer performance, alternative methods should be considered.

‘benchmark’ program When such a program is run on different machines it is possible to make an accurate assessment of the comparative performance of the machines.

Supplementary restraint systems (SRS)

HANDLING SRS COMPONENTS

The following notes are provided to Rover-trained technicians and they are in- cluded here because they contain some valuable advice for all vehicle technicians.

Safety precautions, storage and handling

Airbags and seat belt pre-tensioners are capable of causing serious injury if abused or mishandled The following precautions must be adhered to:

When replacing SRS components in a vehicle, always use genuine new parts and consult the relevant workshop manual beforehand Prior to starting any work on the supplementary restraint system, remove the ignition key, disconnect both battery leads—starting with the earth lead—and wait 10 minutes to allow the DCU backup power circuits to discharge Avoid probing SRS components or harnesses with multi-meter probes unless following an approved diagnostic routine from the manufacturer, and always utilize manufacturer-approved equipment for diagnosing SRS faults Additionally, take care to work away from the direct line of the airbag when connecting or disconnecting multiplug wiring connectors, and never install an SRS component that appears damaged or has been misused.

When handling airbag modules, always ensure they are transported with the cover facing upwards and never carry more than one module at a time Avoid dropping any SRS components and refrain from carrying airbag modules or seat belt pre-tensioners by their wires It is crucial not to tamper with, dismantle, repair, or cut any parts of the supplementary restraint system Additionally, SRS components should never be immersed in fluids, and nothing should be attached to the airbag module cover Always transport airbag modules and seat belt pre-tensioners in the luggage compartment of a vehicle, never in the passenger area.

Storage ž ALWAYS keep SRS components dry. ž ALWAYS store a removed airbag module with the cover facing upwards. ž DO NOT allow anything to rest on the airbag module.

Always store the airbag module or pre-tensioner in the designated storage area, ensuring it is placed on a flat, secure surface Additionally, keep it away from electrical equipment and sources of high temperature to maintain safety and integrity.

Airbag modules and pyrotechnic seat belt pre-tensioners are classified as explosive materials and must be securely stored overnight in a Local Authority-approved steel cabinet.

Disposal of airbag modules and pyrotechnic seatbelt pre-tensioners

Before scrapping a vehicle equipped with undeployed airbags and seat belt pre-tensioners, it is essential to render these safety features inoperable by manually activating them This procedure must be carried out in strict accordance with the manufacturer's instruction manual to ensure safety during disposal.

The coded ignition key

The engine immobilizer system serves as an effective theft deterrent by ensuring that only the uniquely coded ignition key can start the vehicle's engine Key components of this system are illustrated in Fig 8.22.

The transponder chip embedded in the ignition key communicates with the surrounding transponder key coil, enabling electromagnetic interaction This interaction allows the engine control module (ECM) to recognize the key code signal, effectively unlocking the immobilizer and permitting the vehicle to start Additionally, vehicle owners receive a backup key that can reset the system in case the original key is lost.

Fig 8.22 The engine immoblizer system

Fault tracing

Examples of some other techniques that can be of assistance in fault tracing, when used correctly, include the half-split strategy and heuristics.

The half-split strategy, as illustrated in Figure 8.23, effectively minimizes the number of checks needed to identify a circuit defect For instance, if a bulb is confirmed to be functional but fails to light when reinserted, placing a voltmeter in the circuit can reveal whether the fault is located between the fuse input and the lamp's earth Although this method may appear straightforward, its effectiveness extends to more complex circuits, demonstrating its significant utility in circuit troubleshooting.

Fig 8.23 The principle of the half-split method

Heuristics, also referred to as 'rules of thumb', can guide troubleshooting in specific situations For instance, the Xmobile vehicle is known for its starting issues in damp conditions A common solution is to dry out the high-tension (HT) insulation, which often improves the chances of starting Therefore, when responding to a call for a failure to start, it is practical to consider the weather and dry the HT insulation before exploring more complex solutions.

Precautions when working with computer

Before performing any electric welding on a vehicle, ensure the computer is disconnected to prevent damage Avoid exposing the computer to high temperatures, such as those found in bake paint ovens Always discharge static electricity by grounding yourself to protect sensitive components Use high-impedance test instruments to prevent overloading electronic devices Refrain from using chemical cleaners on the ECM, and avoid steam cleaning or high-pressure water jets near it Additionally, confirm that any new units added to the vehicle will not interfere with the computer-controlled systems.

Variable capacitance sensor

A variable capacitance type sensor was introduced in Chapter 5 and the following description provides a little more detail about the principles involved.

Figure 8.24(a) and (b) shows how altering the distance between the capacitor plates changes the value of the capacitance When a variable capacitance is d 1

The substance between the metal plates is known as the dielectric A property of the dielectric is its permittivity e.

Dielectric fills the space between the metal plates. Area = A

Changes in C caused by pressure changes at the sensor thus cause the resonant frequency of the circuit to change The frequency of the AC supply does not change.

If e & A are kept constant and d is changed, the valve of C also changes For example, if d 1 (a) is 5 units and e × A = 50 units, if as in

Resonant frequency of this circuit is approx =

An RLC circuit, as illustrated in Fig 8.24, incorporates a variable-capacitance sensor that influences the frequency at which the voltages across the capacitor and inductor cancel each other out, known as the resonant frequency When the circuit resonates, the voltage across the resistor R aligns with the alternating current (a.c.) supply As the pressure at the sensor alters the capacitance value (C), the terminal voltage (V) at the phase detector circuit becomes directly related to both the resonant frequency and the manifold pressure.

Optoelectronics

Light is composed of discrete elements known as photons, which carry energy that can interact with electrons in specific materials This interaction alters the electronic behavior of the materials, impacting their conductivity, a principle utilized in devices like photodiodes and light-sensitive sensors Additionally, the energy transfer from photons to electrons can generate voltage, forming the foundational principle behind fuel cells.

Figure 8.25 shows the basic principle of an optocoupler This is a device which forms the basis of sensors that are used for position sensing, as in

The steering position sensor, also known as the vehicle speed sensor, operates by directing light from an LED onto a phototransistor, influencing its output When an opaque object interrupts the LED light, the output from the transistor changes accordingly This interruption is facilitated by a rotating disc with holes positioned between the LED and the transistor.

Review questions

1 The piezoelectric generator effect is used in:

2 Manifold absolute pressure in a petrol engine is an accurate indicator of: (a) engine speed?

(d) engine load and a factor in determining air flow in speed density systems?

3 OBD II is mainly concerned with:

(b) vehicles fitted with traction control systems?

(c) making it easier for owner drivers to service their own vehicles?

(d) reducing the fuel consumption of vehicles?

4 If barometric pressure is 1.017 bar and a pressure gauge reads 5.2 bar the absolute pressure is:

5 At the input interface of an ECM, an analogue to digital converter may be used to: (a) reduce the voltage of the input?

(b) convert a voltage reading into a binary-coded word?

(c) slow down the speed of input so that the ECM processor has time to work on it?

6 A twisted nematic material is used:

(a) to reduce cross-talk between cables?

(c) as an anti-knock additive in petrol?

(d) as a sealant to prevent moisture getting into an ECM?

(a) in evaporative emissions control systems?

(b) to provide a reserve supply of fuel?

(c) to allow fuel vapor to be introduced into the exhaust system? (d) to improve the cetane rating of diesel fuel?

(a) the output is 1 when the two inputs are different?

(b) the output is 1 when both inputs are the same?

(c) the output is 1 when both inputs are 1?

(d) the output is 1 when one input is 1 and the other input is zero?

A.1 Companies who supply equipment and diagnostic data

Robert Bosch Ltd, located at PO Box 98, Broadwater Park, Denham, Uxbridge UB9 5HJ, has integrated the code reading and diagnostic functions of the Bosch KTS300 into the KTS500 instruments as of 2001 Other notable companies in the automotive sector include FKI Crypton Ltd at Bristol Road, Bridgewater, Somerset TA9 6BX; the Garage Equipment Association at 2-3 Church Walk, Daventry, Northants NN11 4BL; Gunson Ltd at Acorn House, Coppen Road, Dagenham, Essex RM8 1NU; Haynes Publishing at Sparkford Road, Yeovil, Somerset BA22 7JJ; and Lucas Aftermarket Operations, Test Equipment Division.

9, Monkspath Business Park, Highlands Road, Solihull, West Midlands, B90 4AX. Omitec Instrumentation, Hopton Industrial Estate, London Road, Devizes SN10 2EU Snap-on Tools, Palmer House,154 Cross Street, Sale, Cheshire M33 1AQ.

A.3 OBD II standard fault codes

A principal aim of this book is to show readers that there are significant amounts of technology that are common to all computer controlled automotive systems.

Despite the common ground in automotive diagnostics, the variety of approaches can be puzzling The overwhelming number of diagnostic trouble codes, diverse data access methods, and differing interfaces between scan tools and ECMs complicate the tasks of service technicians This recognition of user challenges throughout a vehicle's lifecycle has led to the integration of various standards into OBD II, with similar standards anticipated for EOBD Key components such as the standard diagnostic plug (SAE J 1962) and the format for diagnostic trouble codes (SAE J 2012) have been discussed in this book.

The following list of standard diagnostic trouble codes is derived from SAE J

In 2012, Robert Bosch Ltd highlighted the significance of diagnostic trouble codes (DTCs) in the USA, with expectations of similar codes in Europe These codes illustrate the benefits of standardization in vehicle diagnostics It is crucial to obtain and interpret these fault codes following the specific instructions provided by the vehicle manufacturer to ensure accurate diagnostics and repairs.

The meaning of these standard codes is described in Chapter 3, section 3.2.2.

OBD II standard fault codes 239

P03XX Ignition System or Misfire

P0300 RANDOM/MULTIPLE CYLINDER MISFIRE DETECTED

P0320 IGNITION/DISTRIBUTOR ENGINE SPEED INPUT

P0321 IGNITION/DISTRIBUTOR ENGINE SPEED INPUT

P0322 IGNITION/DISTRIBUTOR ENGINE SPEED INPUT

P0323 IGNITION/DISTRIBUTOR ENGINE SPEED INPUT

P0325 KNOCK SENSOR 1 CIRCUIT MALFUNCTION (BANK 1

P0326 KNOCK SENSOR 1 CIRCUIT RANGE/PERFORMANCE

P0327 KNOCK SENSOR 1 CIRCUIT LOW INPUT (BANK 1 OR

P0328 KNOCK SENSOR 1 CIRCUIT HIGH INPUT (BANK 1 OR

P0329 KNOCK SENSOR 1 CIRCUIT INPUT INTERMITTENT

P0331 KNOCK SENSOR 2 CIRCUIT RANGE/PERFORMANCE

P0332 KNOCK SENSOR 2 CIRCUIT LOW INPUT (BANK 2)

P0333 KNOCK SENSOR 2 CIRCUIT HIGH INPUT (BANK 2)

P0334 KNOCK SENSOR 2 CIRCUIT INPUT INTERMITTENT

P0337 CRANKSHAFT POSITION SENSOR CIRCUIT LOW

P0338 CRANKSHAFT POSITION SENSOR CIRCUIT HIGH

P0342 CAMSHAFT POSITION SENSOR CIRCUIT LOW INPUT

P0343 CAMSHAFT POSITION SENSOR CIRCUIT HIGH INPUT

P0350 IGNITION COIL PRIMARY/SECONDARY CIRCUIT

P0351 IGNITION COIL A PRIMARY/SECONDARY CIRCUIT

P0352 IGNITION COIL B PRIMARY/SECONDARY CIRCUIT

P0353 IGNITION COIL C PRIMARY/SECONDARY CIRCUIT

P0354 IGNITION COIL D PRIMARY/SECONDARY CIRCUIT

P0355 IGNITION COIL E PRIMARY/SECONDARY CIRCUIT

P0356 IGNITION COIL F PRIMARY/SECONDARY CIRCUIT

OBD II standard fault codes 241

P0357 IGNITION COIL G PRIMARY/SECONDARY CIRCUIT

P0358 IGNITION COIL H PRIMARY/SECONDARY CIRCUIT

P0359 IGNITION COIL I PRIMARY/SECONDARY CIRCUIT

P0360 IGNITION COIL J PRIMARY/SECONDARY CIRCUIT

P0361 IGNITION COIL K PRIMARY/SECONDARY CIRCUIT

P0362 IGNITION COIL L PRIMARY/SECONDARY CIRCUIT

P0370 TIMING REFERENCE SIGNAL ‘‘A’’ HIGH RESPONSE

P0371 TOO MANY HIGH RESOLUTION SIGNAL ‘‘A’’ PULSES

P0372 TOO FEW HIGH RESOLUTION SIGNAL ‘‘A’’ PULSES

P0373 INTERMITTENT/ERRATIC HIGH RESOLUTION SIGNAL

P0374 NO HIGH RESOLUTION SIGNAL ‘‘A’’ PULSES

P0375 TIMING REFERENCE SIGNAL ‘‘B’’ HIGH RESPONSE

P0376 TOO MANY HIGH RESOLUTION SIGNAL ‘‘B’’ PULSES

P0377 TOO FEW HIGH RESOLUTION SIGNAL ‘‘B’’ PULSES

P0378 INTERMITTENT/ERRATIC HIGH RESOLUTION SIGNAL

P0379 NO HIGH RESOLUTION SIGNAL ‘‘B’’ PULSES

P0380 GLOW PLUG/HEATER CIRCUIT MALFUNCTION

P0381 GLOW PLUG/HEATER INDICATOR CIRCUIT

P0400 EXHAUST GAS RECIRCULATION FLOW MALFUNCTION

P0401 EXHAUST GAS RECIRCULATION FLOW INSUFFICIENT

P0402 EXHAUST GAS RECIRCULATION FLOW EXCESSIVE

P0405 EXHAUST GAS RECIRCULATION SENSOR A CIRCUIT

P0406 EXHAUST GAS RECIRCULATION SENSOR A CIRCUIT

P0407 EXHAUST GAS RECIRCULATION SENSOR B CIRCUIT

P0408 EXHAUST GAS RECIRCULATION SENSOR B CIRCUIT

P0410 SECONDARY AIR INJECTION SYSTEM MALFUNCTION

P0411 SECONDARY AIR INJECTION SYSTEM INCORRECT

P0412 SECONDARY AIR INJECTION SYSTEM SWITCHING

P0413 SECONDARY AIR INJECTION SYSTEM SWITCHING

P0414 SECONDARY AIR INJECTION SYSTEM SWITCHING

P0415 SECONDARY AIR INJECTION SYSTEM SWITCHING

P0416 SECONDARY AIR INJECTION SYSTEM SWITCHING

P0417 SECONDARY AIR INJECTION SYSTEM SWITCHING

P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD

P0421 WARM UP CTALYST EFFICIENCY BELOW THRESHOLD

P0422 MAIL CATALYST EFFICIENCY BELOW THRESHOLD

P0423 HEATED CATALYST EFFICIENCY BELOW THRESHOLD

P0430 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD

P0431 WARM UP CATALYST EFFICIENCY BELOW

P0432 MAIL CATALYST EFFICIENCY BELOW THRESHOLD

OBD II standard fault codes 243

P0433 HEATED CATALYST EFFICIENCY BELOW THRESHOLD

P0442 EVAPORATIVE EMISSION CONTROL SYSTEM LEAK

P0443 EVAPORATIVE EMISSION CONTROL SYSTEM PURGE

P0444 EVAPORATIVE EMISSION CONTROL SYSTEM PURGE

P0445 EVAPORATIVE EMISSION CONTROL SYSTEM PURGE

P0446 EVAPORATIVE EMISSION CONTROL SYSTEM VENT

P0447 EVAPORATIVE EMISSION CONTROL SYSTEM VENT

P0448 EVAPORATIVE EMISSION CONTROL SYSTEM VENT

P0455 EVAPORATIVE EMISSION CONTROL SYSTEM LEAK

P0460 FUEL LEVEL SENSOR CIRCUIT MALFUNCTION

P0461 FUEL LEVEL SENSOR CIRCUIT RANGE/

P0462 FUEL LEVEL SENSOR CIRCUIT LOW INPUT

P0463 FUEL LEVEL SENSOR CIRCUIT HIGH INPUT

P0464 FUEL LEVEL SENSOR CIRCUIT INTERMITTENT

P0465 PURGE FLOW SENSOR CIRCUIT MALFUNCTION

P0467 PURGE FLOW SENSOR CIRCUIT LOW INPUT

P0468 PURGE FLOW SENSOR CIRCUIT HIGH INPUT

P0469 PURGE FLOW SENSOR CIRCUIT INTERMITTENT

P0471 EXHAUST PRESSURE SENSOR RANGE/PERFORMANCE

P0475 EXHAUST PRESSURE CONTROL VALVE MALFUNCTION

P0477 EXHAUST PRESSURE CONTROL VALVE LOW

P0478 EXHAUST PRESSURE CONTROL VALVE HIGH

P0479 EXHAUST PRESSURE CONTROL VALVE INTERMITTENT

P05XX Vehicle Speed Control and Idle Control System P0500 VEHICLE SPEED SENSOR MALFUNCTION

P0501 VEHICLE SPEED SENSOR RANGE/PERFORMANCE

P0502 VEHICLE SPEED SENSOR LOW INPUT

P0506 IDLE CONTROL SYSTEM RPM LOWER THAN

P0507 IDLE CONTROL SYSTEM RPM HIGHER THAN

P0532 A/C REFRIGERANT PRESSURE SENSOR CIRCUIT LOW

OBD II standard fault codes 245

P0533 A/C REFRIGERANT PRESSURE SENSOR CIRCUIT HIGH

P0550 POWER STEERING PRESSURE SENSOR CIRCUIT

P0551 POWER STEERING PRESSURE SENSOR CIRCUIT

P0552 POWER STEERING PRESSURE SENSOR CIRCUIT LOW

P0553 POWER STEERING PRESSURE SENSOR CIRCUIT HIGH

P0554 POWER STEERING PRESSURE SENSOR CIRCUIT

P0571 CRUISE/BRAKE SWITCH ‘‘A’’ CIRCUIT MALFUNCTION

P0572 CRUISE/BRAKE SWITCH ‘‘A’’ CIRCUIT LOW

P0573 CRUISE/BRAKE SWITCH ‘‘A’’ CIRCUIT HIGH

P06XX Computer and Output Circuits

P0601 INTERNAL CONTROL MODULE MEMORY CHECK SUM

P0603 INTERNAL CONTROL MODULE KEEP ALIVE MEMORY

P0604 INTERNAL CONTROL MODULE RANDOM ACCESS

P0605 INTERNAL CONTROL MODULE ROM TEST ERROR

P0703 TORQUE CONVERTER/BRAKE SWITCH ‘‘B’’ CIRCUIT

P0704 CLUTCH SWITCH INPUT CIRCUIT MALFUNCTION

P0707 TRANSMISSION RANGE SENSOR CIRCUIT LOW INPUT

P0708 TRANSMISSION RANGE SENSOR CIRCUIT HIGH INPUT

P0715 INPUT TURBINE/SPEED SENSOR CIRCUIT

P0716 INPUT TURBINE/SPEED SENSOR CIRCUIT

P0717 INPUT TURBINE/SPEED SENSOR CIRCUIT NO SIGNAL

P0718 INPUT TURBINE/SPEED SENSOR CIRCUIT

P0719 TORQUE CONVERTER/BRAKE SWITCH ‘‘B’’ CIRCUIT

P0720 OUTPUT SPEED SENSOR CIRCUIT MALFUNCTION

P0722 OUTPUT SPEED SENSOR CIRCUIT NO SIGNAL

P0723 OUTPUT SPEED SENSOR CIRCUIT INTERMITTENT

OBD II standard fault codes 247

P0724 TORQUE CONVERTER/BRAKE SWITCH ‘‘B’’ CIRCUIT

P0725 ENGINE SPEED INPUT CIRCUIT MALFUNCTION

P0727 ENGINE SPEED INPUT CIRCUIT NO SIGNAL

P0728 ENGINE SPEED INPUT CIRCUIT INTERMITTENT

P0742 TORQUE CONVERTER CLUTCH CIRCUIT STUCK ON

P0743 TORQUE CONVERTER CLUTCH CIRCUIT ELECTRICAL

P0746 PRESSURE CONTROL SOLENOID PERFORMANCE OR

P0747 PRESSURE CONTROL SOLENOID STUCK ON

P0751 SHIFT SOLENOID A PERFORMANCE OR STUCK OFF

P0756 SHIFT SOLENOID B PERFORMANCE OR STUCK OFF

P0761 SHIFT SOLENOID C PERFORMANCE OR STUCK OFF

ABS, anti lock braking system 19, 21, 22

To ensure optimal engine performance, it is crucial to conduct an actuator check for injector seat leakage, verify the idle speed valve, and examine the clamping diode Additionally, assessing the current flow in a peak and hold injector and monitoring the driver transistor activation are essential steps Understanding the duty cycle and ensuring a proper earth path, which may include a series resistor, further contribute to effective engine management.

150 electronic unit injectors 163 exhaust gas recirculation valve 18,

The article discusses various components of ignition systems, including 2, 3, and 4 ignition types, as well as the 161 modulator for ABS systems It highlights the operation via serial port 86 and how the ECM pulses the solenoid to create a specific pattern Additionally, it emphasizes the importance of preventing circuit overheating (152) and the role of pulse width modulation (152) in optimizing performance The use of a single point injector (148) and stepper motor (157) is also mentioned, along with the technique of switching to earth (150) for efficient operation.

Back probing 180 Barometric pressure 212 Basic building blocks of electronics 219 Battery condition test using oscilloscope 170

Binary code 40, 45 Breakout box 94 Buffer 46 Burn time 198 Bus (communication) 52

Cables 55 Calibration of test equipment 103 CAN, controller area network 57 Catalytic convertor 179 condition monitoring for OBD II 183

CD ROM 50 Ceramics 134 Charcoal canister 160 Charging system voltage test 170 Checking injection advance angle on a diesel 202

Circuit testing 168 Clamping diode 165 Classes A, B, C 55 Clock 41

Clutch – air conditioning compressor 29 Collect evidence 173

Common technology 1, 38 Compensating wire 142 Compressor 29

Computer (continued) components 40, 41 interfaces 46 memories 48 – 50 performance – millions of instructions per second (MIPS) 227 peripherals 46

Conversion analogue to digital 221 digital to analogue 222

Data input 47 live 86, 98 output 47 parallel 45 serial 45 transfer 45

Diagnostic methods of obtaining fault codes

69 – 71 off board 79 on board 79 procedure 66 self-diagnosis 78 structure of fault codes 80 support services 103 tools 85 trouble codes (DTCs) 65

Digital multimeter 95 current flow test 169 resistance and continuity test 168 voltage drop test 169

Emissions diesel 108 evaporation system 227 exhaust 107 testing 107 Empirical evidence 176 Engine immobilizer system 231 EEPROM 50

EOBD, European on board diagnostics

78, 81, 223 EPROM 50 EVAP, evaporative purge control 224 Exhaust gas composition 107, 132 gas recirculation 154

Fault codes 5, 56 code structure 70, 81 tracing chart 177 Feedback 131, 179 Flash convertor 221 Flight recorder 207 Flip flop 219 Four-bit register 220 Freeze frame 226 Frequency 152 Fuel gallery 12 Fuel pressure regulator 14 Fuel system leakage detector (Figure 8.16) 224

Gates 216, 218 Gateway 53 Gauge pressure 99 vacuum 100 Generic testing ix

Half split method 232 Hall effect 116 – 117 Harness 94

HEGO, heated exhaust gas oxygen sensor 136

Idle speed control diesel 36 petrol 155Ignition map 5

Information that relates exactly to the system 173

IRTE – Institute of Road Transport

Engineers A division of the Society of

Knock checking sensor voltage 187 sensor 119

Manifold absolute pressure meaning of 126 sensor 127 – 130

MIPS, millions of instructions per second

No feedback from oxygen sensor 179

Non-return to zero (NRZ) 57

OBD II a standardized approach to diagnostics 85

Oscilloscope 97 Oxygen sensor comparison between a good sensor and a sluggish one 182 – 183 downstream oxygen sensor 138 in situ voltage test 179 peak-to-peak voltage 182 resistive 137 seeking cause of sluggishness 183 switching characteristics 181 voltaic 132

Partial pressure 212 Piezo electric generator effect 213 motor effect 213 sensor 119 Played back – facility on diagnostic tool 208

Polarized by application of electric field 214

Position of diagnostic port 87 Potential divider (potentiometer) 139 Potentiometer track defective 189 Precautions 186

PROM 50 Protocol 54 Prototype network system 59 Pulse 2

Pulse width modulation (PWM) 152 Pyrotechnic device 228

RAM 50 Ratio air fuel 138 Refrigerant disposal of 30 handling 30 Reluctor ring 7 rotor 2Repair 1, 40Resistive HT leads 200Rising edge 150Road test 98RTL, resistor transistor logic 216