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Student Workbook

LV36 Ignition Systems (3)

kap all phase 2 & 3 6/11/03 11:35 am Page 11

`

Student Workbook for Technical Certificates in

Light Vehicle Maintenance and Repair

Inspection of vacuum and governor

Page

Direct Ignition Systems Diagnosis: 61

Inspection of ignition signal and

Introduction

Within Phase 3 Ignition Systems, we need to look at diagnostic procedures associated with electronic ignition systems To enable this to be achieved, the workbook will incorporate sections from other phases, to be used as a recap before entering into vehicle diagnosis The use of multimeters and basic

diagnosis is taken from Phase 1 Foundation Skills LV02 and short circuit and open circuit diagnosis is taken from Phase 2 Electrical and Electronic Systems LV33 Each of the areas will enable a greater understanding on how to

proceed with ignition system diagnosis

Electrical Measurement Equipment

Selector

10A port

300mA port

volts, ohmsand diodesCommon

Hold / AUTORANGESelector

10A port

300mA port

volts, ohmsand diodesCommonHold / AUTORANGE

As the name suggests, a multimeter is capable of measuring a number of electrical units/values

The selector allows you to choose which value the meter is to measure, such

as ‘Volts DC’ and the ports at the bottom of the meter allow for differing

connections of the multimeter’s leads when necessary (the red lead only has

to be moved when measuring current flow normally)

Every type of multimeter normally has a button that enables the technician to choose the maximum value that he wants to measure (the range of the

meter) On the example shown, this is the yellow button in the middle of the selector Selecting the smallest range for the circuit that you are working on aids accuracy

~ V

A

A

~ A

~ A

Ω

300mV

300mV

Starting from bottom left, the electrical values that this multimeter can typically read are:

Unit multipliers

One amp is equal to one thousand milliamps, which is written as 1A =000mA

One amp is equal to one million micro amps and is written as 1A = 1,000,000

12 v A voltmeter displays thedifferencein voltage

between where you put the red probe and where you put the black probe

0 v

0 v

12 v A voltmeter displays the in voltage

between where you put the red probe and where you put the black probe

Never connect an ammeter across a resistance; a good

ammeter has zero internal resistance

Remember:

series

always fit an ammeter

in with the circuit

Remember:

•Always switch the circuit OFF first

• Always disconnect the

component from the remainder of the circuit Close switch

0.00Ω

14.4Ω 14.4Ω 14.4Ω

Remember:

•Always switch the circuit OFF first

• Always disconnect the

component from the remainder of the circuit Close switch

Remember:

•Always switch the circuit OFF first

• Always disconnect the

component from the remainder of the circuit Close switch

0.00Ω

An ohmmeter (a multimeter with ohms selected) is always fitted across the component or wire that you want to test Current must not be flowing in the part of the circuit that you are testing as this will seriously affect your readings

An ohmmeter measures circuit resistance by applying a known voltage to a circuit from a battery inside its case and measuring the resultant current flow – from these two values it can calculate the resistance using Ohm’s Law in the same way that you have If current is flowing in the circuit from a different source (i.e the vehicle battery) this will seriously affect its calculation

An ammeter (a multimeter with amps selected) must be fitted in series with the circuit whose current you want to measure

This means that the circuit must be broken and the ammeter must be put into the circuit A good ammeter has an extremely small internal resistance so it is important that you take care not to short a circuit out by putting the ammeter across the only resistance in a circuit (provide the current with an easier path

to take through the meter) This will at best blow a fuse in the meter and at worst set it alight!

General fault finding procedures

Diagnosis is a significant part of a vehicle technician’s responsibility With the proliferation of electrical systems on a modern vehicle, an ability to diagnose electrical faults quickly and accurately has become most valued

To be able to fault diagnose electrical circuits accurately and quickly, an understanding of voltage is critical This coupled with the correct use of a voltmeter will enable a technician to find virtually any fault

Voltage

A few voltage rules must be understood and remembered:

Voltage is electrical pressure – it ‘pushes’ current around a circuit

Voltage will drop across a resistor

Volts drop will only occur if current is flowing

The amount the voltage drops across a resistor in a circuit is dictated by the comparative value of that resistor i.e its value when compared to that of any other resistors in the circuit The bigger the value of a resistor, the greater the amount of the available voltage will be used by it when compared to the other resistors in the circuit

The voltage after the last resistor in a circuit will be 0 volts so long as current can flow

If there is only one resistor in a circuit it is also the last resistor and therefore the voltage after it will be zero so long as current is flowing

A voltmeter displays the difference in voltage between the position of the red and black probes

Electrical faults

To recap, there are three main types of electrical faults These are:

1 Open circuit faults:

2 High resistance faults, and

3 Short circuit faults

Open circuit faults

This fault causes an incomplete electrical circuit in which no current flows

High resistance faults

This fault causes the reduction in the flow of electrical current through a circuit component

Short circuit faults

This is a faulty or accidental connection between two points of different

potential in an electrical circuit caused by pushing the load and establishing a path of low resistance through which an excessive current can flow It can cause damage to the components if the circuit is not protected by a fuse

This will result in a blown fuse, popped circuit breaker or a serious fire!

Because the short to ground has reduced the circuit resistance to virtually nothing, there is no limiting factor to the amount of current that the battery will produce (except the battery’s amp hour rating) This will result in a serious excess of circuit in the affected circuit

After the resistance and after the switch (earth switched circuit)

This is probably the best kind of short circuit fault as it is not actually a fault!

In fact, it can be considered something of a bonus because if the proper earth for the circuit should develop a problem (such as a resistance build up at the earthing bolt) we have our ‘fault’ to fall back on!

After the resistance but before the switch (earth switched circuit)

This means that the driver cannot switch off the affected circuit The

resistance has its usual permanent supply but it now has a permanent earth, courtesy of the fault If the circuit is one where the consumer (lamp for

example) is not normally visible to the driver – such as a luggage

compartment light – the driver will complain that the battery keeps going flat This type of short circuit is known as a ‘parasitic drain’ fault as the affected circuit is draining the battery (like a parasite)

Inspection and Other Fault-Finding Techniques

Don’t rush in!

Charging into diagnosis is seldom productive Working too quickly and

without logical thought can lead to missing the simple, obvious faults that would be identified had a more logical structured approach been taken

initially With complex systems, a well-structured, logical approach should be taken This approach should be adhered to throughout diagnosis (simple or difficult) and in most cases the same approach can be used time and again

Driver interrogation

The driver of the vehicle probably knows more about the vehicle’s history than anyone else and they normally have first hand knowledge of the fault If a vehicle develops a fault, simple or complex, the driver will have sensed more

of the symptoms than the technician can during workshop diagnosis It is therefore important to ask the driver the correct types of questions before they leave the vehicle workshop The driver’s comments can prove valuable, especially with an intermittent fault, which is often difficult to locate

If the correct types of questions are asked initially, the answers can usually save time by preventing unnecessary diagnostic routines The customer is normally willing to supply the information, so why not allow the customer to provide you with the information you require to ease fault diagnosis?

By gathering information on the problematic system, you can identify a logical diagnostic sequence that will help you to identify the fault By checking and testing strategic parts of the circuit, you can quickly reduce the size of the area that you need to concentrate on

You may think that you need a large amount of data and information before you start fault diagnosis, but by viewing a circuit diagram, you can eliminate certain sections of the circuit and therefore not require all the information initially believed necessary

EARTH

IGN

IDLE

ECM VOLTS

INJ

MAP

TPS

Build the puzzle until one of the pieces is missing or doesn't fit

Refer back to the information and the diagnostic sequence throughout your test routine You may have to follow a different route if the components are too difficult to access or your findings are not as you had first thought

Visual inspection

Always be prepared to change or re-think your strategy

Aural inspection

Many technicians become confused when diagnosing complex electronic system faults If there is insufficient information and the technician has limited knowledge, guesswork can take over The technician will often condemn a component that they do not fully understand, and may make a diagnosis by looking at the quantity of the suspect component that the parts department sells; this leads to the parts person diagnosing the fault! This is a potentially expensive (and embarrassing) strategy to adopt, as many parts departments will not allow a workshop to return parts once purchased

If the new part ordered is not required (the guess was incorrect) the price of the part has to be absorbed by one of the parties, workshop or customer When the price of the part is low e.g £10.00, the amount can usually be absorbed into the vehicle diagnosis time However, when the price of the part

is high e.g £200.00, the cost cannot normally be absorbed by the customer and the cost has to be absorbed by the workshop - reducing profit If this happens on several occasions, confidence is lost and electrical/electronic diagnosis is then often contracted to other third party businesses - expensive! The reduction of such work in a workshop will quickly lead to de-skilling of the technical staff Technicians need to undergo regular training throughout their workshop life to allow them to service and repair the modern motor vehicle

When formulating your diagnostic strategy, ensure that you prioritise the checking of the obvious first When the electrical circuit being tested has an ECM, there is often a tendency to over complicate matters

Many workshops do not have equipment capable of testing complex electronic components (e.g ECM or similar); there is therefore a tendency to assume that the remainder of the circuit is also complex

There may be an electronic component at the centre of the circuit but the remainder usually consists of general electrical items that can be tested with

an ordinary multimeter (bulbs, switches etc)

From knowledge gained over previous electrical and electronic courses, it should now be clear that although modern electrical circuits are often fitted with electronic control modules, the testing of such circuits still requires similar skills to that of simple electrical circuits If we assume things are more

complex than in reality, we can find ourselves very frustrated if the fault is not initially obvious

Road test

Record your results as you carry out your tests By recording the test results

at each stage (correct or incorrect), you can review your diagnostic plan at any time Then if for any reason you are interrupted, you can come back to it later and recall the results instantly A record of the test results will also assist

if another person is to continue where you left off, rather than needlessly repeating checks

Diagnostic information is often difficult to access in the independent repair market and this type of information can be very valuable If information and data is collated every time a repair is carried out; whether it is information from repair manuals, information printed off test equipment or data gathered during test procedures, this could be used to construct an effective diagnostic library Few people are blessed with a photographic memory! It may take a little time

to set up in the first instance, but over a short period the library will grow into a very large, in-depth point of reference

Some of the information that you can obtain from test equipment data list print-outs is unavailable from technical information suppliers and therefore a serviceable vehicle is a unique source of valuable data If the information is good or even bad (an idea is to highlight the bad data) the data can be used

as a comparison against vehicles to be repaired in the future

A simple PC is capable of providing an effective database utility at very little cost The information can then be catalogued into various categories and quickly referenced

This approach is virtually guaranteed to increase productivity and profitability over time

Diagnosis without a Code Reader

The previous section has looked at diagnostic techniques that will help all technicians with the solving of both complex and non-complex system faults Within this section a more formal process will be explained This process will look at solving faults using diagnostic codes if present, but without the use of

a code reader The material used for this diagnostic process is from a

Japanese manufacturer, although most manufacturers will have similar

diagnostic material available

Step one of the process involves questioning the customer regarding the fault that they have reported As described earlier the customer is the best person

to explain what the fault is and when it happens Pre diagnostic question forms are available, but the service staff at the front desk usually use them If possible the technician who is going to be carrying out the task should speak

to the customer, this eliminates the possibility of the message being passed

on incorrectly

Step two of the process relates to the checking of diagnostic codes Each manufacturer will have a different way of doing this, although most vehicles have the facility to check the codes without a code reader This usually

involves shorting out two of the terminals within the diagnostic plug, and then counting the sequence flashes outputted by the engine, or diagnostic warning light When the codes have been collected they should be recorded so that they can be used if needed later in the diagnosis process

PRE-DIAGNOSTIC QUESTIONING

CHECK CODES (TE1-E1) CHECK CODES (TE1-E1)

CLEAR DIAGNOSTIC CODES

To complete step three the codes need to be cleared Again, different

manufacturers will have different way of doing this although disconnecting the battery for approximately 90 seconds will usually clear the codes The reason that the codes need to be cleared is that other technicians may have

attempted to fix the vehicle While attempting to do this they may have

disconnected different sensors looking for the fault, each time that a sensor is disconnected a code will register within the electronic control unit If as a technician you try and diagnose all the codes outputted, then the diagnostic process will be lengthened and tests will be carried out on systems that are not faulty

PRE-DIAGNOSTIC QUESTIONING

?….What Happens Next….?

CHECK CODES (TE1-E1) CHECK CODES (TE1-E1)

CLEAR DIAGNOSTIC CODES

SET TEST MODE (TE2-E1) SET TEST MODE (TE2-E1)

CONFIRM FAULT (ROAD TEST)

Steps four and five are linked, as the vehicle now needs to be placed in test mode (if the manufacturers’ system allows this), and then road tested to

simulate the fault By placing the vehicle in test mode the electronic control unit becomes more sensitive Many manufacturers use two trip logic when the electronic control unit is retrieving information from the sensors This means that the fault needs to happen twice before the engine control unit puts

on the diagnostic warning light When placed in test mode the fault only

needs to occur once and a code will be registered within the electronic control unit

When the road test has been completed the electronic control unit needs to be interrogated for any codes that are present and this take the form of step six

If a code is present then the next phase of the diagnostic process will take place

To complete step seven, the system relating to the code outputted needs to

be diagnosed Again as before, each manufacturer will have their own

diagnosis process to enable the technicians to complete this phase As an example, a page has been taken from the engine manual of a Japanese manufacturer This same manual would then be used to extract the correct diagnostic process If no literature is available on the vehicle, then the

technician will need to draw on information gained from various phases of their training, to give them an understanding of how the system works Most

of the codes used by the different manufacturers are generic, so even if the manufacturers’ manuals are not available, the technician should be able to use the code to point him in the correct direction

When the faulty system has been repaired the vehicle needs to be road tested again (before the road test the codes should again be cleared) This enables the technician to confirm that the vehicle has been repaired and the fault no longer occurs After the final road test has been carried out the electronic control unit should be rechecked for codes as this will help confirm that the fault has been rectified

This process can be used for any occasions where diagnostic codes are present But what if there are no codes present? The process for diagnosing faults when there are no codes present is not that different The process will take the format as described in the inspection and other fault finding

techniques One important introduction is the carrying out of basic

inspections; these involve the testing of the following systems:

CHECK DIAGNOSTIC CODE

DIAGNOSE THE CIRCUIT

REPAIR THE FAULT

CONFIRM REPAIR (ROAD TEST)

JOB DONE

• emission system (using four gas analyser)

The order in which these systems are checked will depend on the type of fault that has occurred Some manufacturers incorporate faultfinding charts within their vehicle manuals These charts will help the technicians to head in the right direction for a given fault, and not start testing systems that have no relevance An example of this has been taken from the symptom chart of one

of the major manufacturers The vehicle fault is that the vehicle does not start (there is no initial combustion) The system chart point to four possible areas:

• ECU power source

• ignition coil (with module) circuit

• fuel pump control circuit

• injector circuit

The fault can now be simulated and each of these systems checked When simulating faults, it may not be possible to do it on the road, as you may need the vehicle in the workshop with the appropriate test equipment Various faults can be simulated within the workshop and the two diagrams above demonstrate this

Circuit voltages

Engine ECU Terminals

After you have completed the simulation, and the system at fault has been identified then information on that system will need to be accessed

Depending on the vehicle and the technical information available to the

technician, the faulty system can then be checked, and diagnosed Examples given are of the types of technical material that is available to help in the diagnostic process

JOB DONE CONFIRM REPAIR (ROAD TEST)

REPAIR FAULT SYSTEM INFORMATION SYMPTOM SIMULATION

NORMAL CODE BASIC INSPECTIONS SYMPTOM CHART

SYSTEM INFORMATION SYMPTOM SIMULATION

NORMAL CODE BASIC INSPECTIONS SYMPTOM CHART

NORMAL CODE BASIC INSPECTIONS SYMPTOM CHART

With the correct system identified and all the checks carried out, the fault then needs to be rectified After rectifying the fault the codes should again be cleared The vehicle then needs to be road tested to confirm that the

operation of the vehicle is correct After the road test the codes need to be checked again, if no codes are present then the vehicle can be returned to the customer

Progress check 1

Answer the following questions:

1 What is the name of the component that is used to measure

Voltage/Amperage and Resistance?

2 If an electrical circuit is said to be "open circuit" What does this mean?

3 After checking the diagnostic codes why should they be cleared?

4 What type of electrical faults will cause the engine to crank, but not start?

Code Readers

Each manufacturer will have their version of a code reader/tester, specifically for diagnosing faults on their own vehicles With the introduction of data link connectors now fitted to all vehicles, it is possible for an independent

manufacturer to produce generic code readers These code readers will access many different vehicles across a range of manufacturers, enabling even small garages to have access to the vehicles diagnostic codes for use in vehicle diagnosis Although non-franchised dealerships will have access to the diagnostic codes, it may still be necessary to obtain the manufacturer’s literature to assist the technician in the diagnostic process

Within Phase 3 Ignition Systems we will look at the code reader designed by sun/snap-on (Modis) Selected pages have been taken from the operator’s manual to give an overview on what types of feature are available on code readers/testers When diagnosing ignition systems faults the scope feature provided can be invaluable

MODIS™

The Modular Diagnostic Information System (MODIS™) is a hand-held unit designed to host various tools and accessories used in the automotive repair industry Its open architecture platform utilises integrated vehicle testing instruments and information

MODIS™ features an on-board diagnostic module that interrogates the

numerous on-board electronic systems in the vehicle, and provides expert guidance to assist you in resolving symptoms, codes, or complaints

Additional integrated measurement modules enables you to obtain exact measurements of identified problematic components, connectors, or systems

MODIS™ easily accommodates future enhancements and various plug-ins

that allow you to configure the system to meet specific needs

Main menu

The Main Menu screen consists of screen buttons that appear in a vertical column on the left side of the screen Selecting one of these screen buttons activates:

• a currently installed module

• the Status Bar at the bottom of the screen

On initial start-up, one of the menu selections is highlighted indicating the current active area of the screen

For detailed information on menu items that are specific to a plug-in module, refer to the relevant manual for that module

Scanner

This menu allows MODIS™ to operate as a fully functional scan tool on the

vehicle ECU

The functions of this menu are available only when the Scanner Plug-In

Module is installed It states error messages, trouble code definitions, data read-outs It also performs specific tests on the vehicle under test In the

Scanner Plug-In Module manual, refer to the introductionsection

Multimeter

This menu allows MODIS™ to operate as a graphical multimeter to measure

volts, amps and ohms Specific setup instructions are provided on screen The functions of this menu are available only when the Lab Scope Plug-in Module is installed

In the Lab Scope Plug-in Module manual, refer to the introduction section

Scope

This menu allows MODIS™ to operate as a 4 channel lab scope

The functions of this menu are available only when the Lab Scope Plug-in Module is installed

In the Lab Scope Plug-in Module manual, refer to the introduction section

Select any of the other modes that will trigger the Snapshot to be taken

automatically if the condition set is met:

Select to state the ignition system of the vehicle under test

To calculate RPM, it is necessary to identify the ignition system and method of

connection for the RPM lead That way the Lab Scope Plug-in Module can

calculate the RPM division factor for the vehicle under test

Select to set Ignition Type:

Select if the ignition system of the vehicle under test is not stated above:

a Connect to a plug or coil wire

b Set the RPM factor to display the correct RPM

Progress check 2

Complete the following:

Below is a selection of slides from the power point presentation, identifying the process of diagnosing a fault with the assistance of a code reader Make notes from the presentation identifying the key differences

P011 5……

P122 4

D ata lis t

P011 5……

P122 4

D ata lis t

PRE-DIAGNOSTIC QUESTIONING

CHECK DTC / FREEZE FRAME DATA

?….What Happens Next….?

CONFIRM FAULT (ROAD TEST)

PRE-DIAGNOSTIC QUESTIONING

CHECK DTC / FREEZE FRAME DATA

CLEAR DIAGNOSTIC CODES

VISUAL INSPECTION

SET TEST / CHECK MODE /

DATALIST SNAPSHOT

PRE-DIAGNOSTIC QUESTIONING

CHECK DTC / FREEZE FRAME DATA

CLEAR DIAGNOSTIC CODES

Ring For Support

Oscilloscope

Throughout this phase descriptions have been given on different methods of diagnosing non-complex and complex system faults Each of these methods will assist the technician to diagnose the ignition system quickly and

accurately Most modern code readers will have an oscilloscope function that can be used to identify the signals sent from the electronic control unit to operate the ignition system If a modern code reader is not available then an independent oscilloscope can be used to identify these signals To use an oscilloscope, a basic understanding of how it is operated will need to be achieved

Within this section a description on how an oscilloscope generates the

waveform and displays it will be covered Also a brief description will be given

on some of the controls that enable the technician to display the waveform, although a practical exercise is advisable to give a greater understanding