Toyota training diagnostic techiques and tools

Temp Sensor Combination Switch Voltage ON/OFF Oxygen Sensor Variable Voltage Voltage Pulse Pattern Active Speed Sensor MRE A MRE B Sensor IC Exhaust Gas Signals from switches and sens

• Electronic Control Units

• Logic Function

• Simple ECU Inputs

• Simple ECU Outputs

• Self-Diagnosis

• Memory

• Customization

• Initialization

Section 1 Topics

Electronic Control Units

Electronic Control Units

Electronic Control Units

(ECUs)are small

computers programmed to

perform specific

automotive functions

ECUs use electronic components in integrated circuits to perform their functions

What are some typical

automotive ECUs?

In the 1970’s, the decreasing cost and increasing power of computerized

microprocessorslaunched the personal computer industry Because of their speed and flexibility in carrying out complex functions, microprocessors were adapted for hundreds of uses beyond personal computers

The first microprocessors began appearing in automotive engine control systems in the early 1980s In automotive applications, they became known

as electronic control units (ECUs) Today, some vehicles may have

dozens of ECUs controlling a wide variety of vehicle systems, including:

• engine controls

• transmission

• braking

• steering

• air conditioning

• door locks

• suspension

• cruise control

• tire pressure monitoring

Electronic

Control Units

ECU Logic Function

ECUs have electronic logic circuits that “make decisions”

by evaluating conditions according to predetermined rules.

Light Control SW Light Control Sensor

Headlights

Taillights Body ECU

IF

Light control switch is in the AUTO position and

Light control sensor detects LOW ambient light and

Ignition switch is ON

THEN

Turn headlights ON Turn taillights ON

An ECU is a small computer programmed to perform a specialized function in the vehicle As with any computer, it operates on the principle of input, processing, and output

Input –Information about conditions is supplied to the ECU as input signals Input can be provided by:

• sensors

• switches

• other ECUs

Processing– The ECU analyzes the input signals Based on its programming, it determines what output signals to send, if any

Output– Vehicle systems are controlled by the ECU output signals These signals may cause a motor to operate, a light to come on, or some other operation of a vehicle component

For an example of the ECU’s logic function, consider the lighting control system which is within the Body ECU A simple lighting control system uses three inputs – the light control switch, the light control sensor, and the ignition switch

When the condition of these three inputs matches the conditions preprogrammed in the ECU, the ECU turns on the headlights and taillights

Logic Function

How ECUs

Work

Simple ECU Inputs

Variable Resistance

What are some other

types or examples of

ECU inputs?

Temp Sensor

Combination Switch

Voltage ON/OFF

Oxygen Sensor

Variable Voltage

Voltage Pulse Pattern

Active Speed Sensor

MRE A MRE B Sensor IC

Exhaust Gas

Signals from switches and sensors can supply information to the ECU in several ways

Voltage ON/OFF– A simple switch opens or closes a circuit It is the presence or absence of voltage in the circuit that signals the ECU

Variable Voltage – Some sensors produce a voltage that changes depending on the conditions the sensor is measuring The amount of voltage produced at any given moment provides information about the condition at that time

Variable Resistance– In other types of sensors, electrical resistance increases or decreases as external conditions change Sensing the changing voltage as a result of changing resistance in the circuit signals the ECU what the conditions are

Variable Pulse Pattern– Another method for signaling the ECU about changing conditions is to turn a circuit on and off rapidly at a particular frequency This works especially well for signaling rotational speed It is the frequency of the ON/OFF pulses that supplies information to the ECU

Simple ECU

Inputs

Voltage ON/OFF (Switch) Input

OFF: V = 12.6V

(open circuit voltage)

Ground-side switched

ON: V = 0.1V

(available voltage)

Voltage can also be measured

at the ECU terminal

The ECU detects the state of a ground-side switch by reading the

circuit voltage

When switch ON is detected, the ECU performs a function, such as turning on a lamp

* Conceptual illustration only

0V

The diagrams above illustrate a ground-side switch connected to an ECU

The ECU supplies battery voltage to the switch circuit and provides the circuit’s load (a resistor) The ECU’s electronic circuits detect when the voltage after the load is high (near battery voltage) or low (near ground voltage)

While the switch is open, no current is flowing and the available voltage after the load is near battery voltage When the switch is closed, current flows and most of the battery voltage is dropped across the load The available voltage after the load is now near ground voltage

In this example, the switch controls a lamp, but is not actually part of the lamp circuit When the ECU senses a voltage drop in the switch circuit, it supplies five volts to the transistor This in turn closes the lamp circuit, lighting the lamp

You can detect the same high or low voltage the ECU is detecting by measuring voltage at the appropriate ECU terminal If the switch is closed and the voltage remains high, you’ll know there is an open in the circuit between the ECU and the switch

The actual wiring inside the ECU is extremely complex The ECU circuit details shown in the diagrams above and the diagrams on the following pages are to illustrate concepts, not actual internal connections.

Voltage ON/OFF

(Switch) Input

NOTE SERVICE TIP

Variable Voltage Input

The oxygen sensor is a voltage generator.

V> 0.45v : air-fuel ratio too rich

V= 0.45v : air-fuel ratio correct

V< 0.45v : air-fuel ratio too lean

Atmosphere

Voltage

The engine control module

interprets the voltage to make

corrections to the air-fuel ratio

V

Exhaust Gas

An oxygen sensor is a voltage generator, producing between 0.1v and 0.9v

depending on the oxygen content of the exhaust gas compared to the atmosphere

The engine control module’s electronic circuits measure the amount of voltage generated by the oxygen sensor, and use that information to control the air-fuel ratio

Variable Voltage

Input

Variable Resistance Input

A temperature sensor is a type of variable resistor.

Its resistance changes with temperature

12.6V or 5V

An ECU can detect the change

in the sensor’s resistance by measuring voltage

ECU

V

A temperature sensor is a type of variable resistor whose resistance changes with temperature This type of sensor is often called a thermistor

Two types of thermistor are:

Positive temperature coefficient (PTC) thermistor– resistance increases

as temperature increases

Negative temperature coefficient (NTC) thermistor– resistance decreases as temperature increases

Thermistors are commonly used for engine coolant temperature sensors and ambient temperature sensors Modern Toyota vehicles use NTC thermistors exclusively

Variable Resistance Input

Pulse Pattern Input

An active wheel speed sensor generates a series of voltage pulses

as the wheel rotates

As rotation speed increases, pulses are generated at a higher frequency

Lower Rotation Speed

Voltage

Time

Voltage

Time

Higher Rotation Speed

The ECU measures the pulse frequency

to calculate vehicle speed

MRE A MRE B Sensor IC

Another type of ECU input is a pulse pattern When voltage rises

momentarily, then falls, the transient voltage reading is called a pulse When

a component creates multiple pulses, the result is a pulse pattern (or pulse

train)

An active wheel speed sensor is a component that generates a pulse pattern

A magnetic ring mounted on the wheel hub has alternating north-south fields that are detected by the sensor pickup As the wheel rotates, the alternating magnetic fields are converted into a series of voltage pulses The frequency

of the pulses increases with the wheel rotation speed

When the pulse pattern is provided as ECU input, the ECU’s circuits are able

to measure the pulse frequency and calculate wheel RPM and vehicle

speed

Pulse Pattern

Input

See Appendix for More Info

A

Simple ECU Outputs

When the operating conditions are met, the ECU makes a

connection to power or ground to energize a circuit

B+

ECU

Transistor

Ground-side controlled circuit

Power-side controlled circuit

Collector

Base

Emitter

How a Transistor Works (NPN)

When voltage

is applied to the base…

current can flow from the collector to the emitter

ECU

B+

5V

PNP

NPN

The simplest way for an ECU to control a vehicle function is to turn a circuit

on or off A circuit can be ground-side switched or power-side switched

Electronic circuits use transistors for switching circuits on and off A

transistor is a solid-state electronic component having a base, collector and emitter In the more commonly used NPN transistor, when sufficient voltage

is applied to the base, current flows from the collector to the emitter

One of the advantages of the transistor is that a low voltage at the base is able to control a large current flowing through the collector and emitter In that respect, a transistor is similar to a relay

Some transistors also regulate current flow based on the amount of voltage applied to the base Within the transistor’s limits, a higher base voltage results in a greater flow of current through the collector/emitter This feature

is used in amplifier circuits where the low voltage signal from a microphone regulates current flow in higher power speaker circuits

Simple ECU

Outputs

Transistors as

Switches

Pulse Width Modulation

The ECU can open and close a circuit rapidly to control

component operation

The process of varying the amount of time a circuit is ON is called pulse width

modulation

The ECM regulates the injector

ON time by regulating the width of the voltage pulse to the injectors

Notice the pulse width increases at higher load as the ECM increases the injector ON time

Voltage Pulses

Example

Pulse Width

An ECU’s electronic circuits have the ability to open and close a circuit very rapidly The ECU can switch a circuit on for a fraction of a second at very precise intervals

When a circuit is switched ON and then OFF, the momentary change in voltage

creates a voltage pulse (The pulse can be either a momentary increase or

decrease in voltage depending on whether the circuit is ground-side switched

or power-side switched and where the voltage is measured.) When the voltage is viewed on an oscilloscope, the voltage pulse’s width represents the amount of time the circuit is switched ON and can be as brief as

1 millisecond or less In some circuits, the ECU uses the amount of ON time to regulate component operation

When the ECU varies the width of the voltage pulse (the ON time) to control a

component, the process is called pulse-width modulation.

In the above example, the frequency of the pulses changes as well as the

pulse width In some circuits, the frequency of the pulses is constant

Pulse Width

Modulation

NOTE

Measuring Duty Cycle

When the ECU modulates a circuit at a constant frequency, you can measure

the circuit’s duty cycle Duty cycle is the percentage of ON time compared to

total cycle time.

B+

ECU

12 V

75% ON (grounded)

0 V

Varying the duty cycle can vary the brightness of a lamp

or the speed of a motor

12 V

0 V

If the percentage of ON time decreases, the lamp becomes dimmer

In a ground-side controlled circuit, measure after the load.

5V

1 cycle (100%)

25% ON (grounded)

1 cycle (100%)

The terms pulse-width modulation and duty cycle are often confused or

used incorrectly

Pulse-width modulationis a function an ECU can perform to turn a circuit on and off rapidly to regulate the amount of ON time As the pulse width changes, the frequency of the pulses might or might not change depending on the circuit design and intended operation

When a circuit is switched on and off rapidly at a constant frequency, duty

cyclemeasures the percentage of ON time compared to total cycle time If the circuit is ON 75% of the time, it is operating at a 75% duty cycle When a circuit

is duty-cycle controlled, the pulse frequency does not change – only the percentage of ON time

An ECU varies the duty cycle to control the speed of a motor or the brightness

of a lamp by switching the circuit ON and OFF hundreds of times per second Human senses can’t perceive a lamp or motor being cycled on and off that quickly Nonetheless, the amount of power to the component increases or decreases depending on how much of the time the circuit is ON versus OFF

As OFF time increases, the net power supplied to a component decreases resulting in the lamp becoming dimmer or the motor running slower As ON time increases, power increases and the lamp becomes brighter or the motor runs faster

When the circuit is ground-side controlled, voltage before the load is always

Duty Cycle

NOTE

Measuring Duty Cycle

Signals in a power-side controlled circuit are the opposite of

signals in a ground-side controlled circuit

75% ON (powered)

In a power-side controlled circuit, measure before the load.

B+

If the percentage of ON time decreases, the lamp becomes dimmer

25% ON (powered)

1 cycle (100%)

1 cycle (100%)

ECU

Most circuits in Toyota vehicles are ground-side controlled When a pulse-width modulated circuit is power-side controlled, the voltage modulation is observable after the ECU and before the load In this arrangement, the circuit is ON when the voltage rises

Note that if voltage is measured after the load, a very minute change in voltage occurs as the circuit is modulated At this point in the circuit, voltage is zero when the circuit is open When the circuit is closed, ground voltage is present The difference is usually less than 0.1V and may not be observable depending on your scope settings

Power-Side

Control

The ECU’s internal wiring can be arranged so it can detect

when an input circuit is open or shorted to ground.

Throttle Position Sensor

ECM

VTA

VTA2 VC

E2

Under normal conditions, the ECM senses more than 0V and less than 5V at VTA and VTA2

5V

2002 Tundra V8

DTC P0120 Throttle/Pedal Position Sensor/Switch “A”

Circuit Malfunction

With either a short or an open in the input circuit, voltage at VTA and VTA2 becomes 0V and the ECU sets a DTC

A significant reason ECUs have become so common in automobile systems

is their ability to perform self-diagnosis ECUs can identify faults in circuits,

components, and even within the ECU itself When a fault is detected, the ECU can:

• Illuminate a warning light

• Set a diagnostic trouble code

• Begin operating in a fail-safe mode by:

◦ Disabling a system that is working incorrectly

◦ Using sensor data from alternate sources

◦ Applying alternate rules for operating the vehicle or subsystem

to maintain maximum safety

An ECU’s self-diagnosis capabilities can range from very simple to highly sophisticated Each ECU has its own features and limitations, and very few work in exactly the same way

The example above is a throttle position sensor circuit The electronics inside the engine control module (ECM) are designed so that an open or a short to ground on VTA or VTA2 can be detected and a DTC set The circuit arrangement inside the ECM is not able to distinguish a short from an open, however In either case, the voltage the ECM is monitoring goes to 0V

Self-Diagnosis

Differences in

Self-Diagnosis