Introduction to Vehicle Electronic Systems and

Fault DiagnosisAPTE7504 – Vehicle Electronic Diagnosis

Week 1Praneel Chand

Vehicle Systems• Motor vehicles remain fundamentally unchanged e.g. engines have

pistons, brakes have discs or drum, suspension has springs etc• Much of the work done by service technicians is traditional – checking

brakes, oil and filter change etc• Service work is done to avoid faults or diagnose car owner problems • Just because modern cars are fitted with electronic devices, it doesn’t

mean they can’t be remedied or assumed that they are the cause of the problem

Vehicle Systems (cont)• Typical service tasks for modern car

shows ‘traditional’ nature of work• If a technician does this properly –

safely, methodically & thoroughly, with proper checks at appropriate stages,• He/she possesses some important

attributes needed to service or diagnose electronically controlled systems

Service task list [1]

Basic Components of Vehicle Electronic Systems• A typical vehicle electronic system has

some basic elements• Electronic control unit (ECU)• Sensors• Actuators• Cables (connecting the elements together)

• There are many types of electronic systems in a vehicle body• Door & lighting systems, battery

management, climate control, ABS, traction control, ESP, smart airbags, etc• You will learn these systems in depth in

weeks 5-8

Computer

ActuatorsSensors

Processing

Cables

Inputs Outputs

Basic elements of an electronic system

Basic Components of Vehicle Electronic Systems - ECUs• ECU is central to the operation of the system because it holds the

computing capacity to enable the system to function• Several ECUs are linked to each other via a communications network• Knowledge of ECUs and how they operate is important for vehicle

electronic system diagnosis• You will learn about this in week 2

Basic Components of Vehicle Electronic Systems - Sensors• Devices that ‘sense’ some physical quantity and produce an electrical

response to represent the quantity• E.g. wheel speed sensors in ABS• By looking at samples of types of sensors, general knowledge of

sensors needed for examining and troubleshooting can be obtained• You will learn about this in week 4

Basic Components of Vehicle Electronic Systems - Actuators• In vehicles these are usually electro-mechanical devices which use the

electrical outputs from the ECU to perform tasks or actions• E.g. a solenoid can be used in a cruise control actuator• Some actuators are purely electrical e.g. transistors and relays in

lighting systems• By looking at samples of types of actuators, general knowledge of

actuators needed for examining and troubleshooting can be obtained• You will learn about this in week 4

Basic Components of Vehicle Electronic Systems – Student Activity 1

• In groups, discuss some other elements/components which you think are needed in vehicle electronic systems

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Electronic System Diagnosis and Repair• Individual components such as ECU, some sensors and actuators are

not designed to be repaired in garages• Main function of technician is to determine the defective component

in the system and replace that component correctly.• Actual method for testing depends on the diagnostic system of the

car• Onboard diagnostics (e.g. OBDII scan tools) or off-board diagnostics

e.g. oscilloscopes or multimeters or a mix of both can be used• You will learn about scan tools and scopes in Week 3.

Electronic System Diagnosis and Repair• Diagnostic systems point the operator to an area in which the defect

lies. It does not necessarily mean that a particular component in system is defective• It is important to be methodical and unwise to start testing things

randomly or try changing parts in the hope to fix the problem by chance• In short, the necessary knowledge for diagnostics is in two parts:• An understanding of the system in which the problem exists• The ability to apply a logical diagnostic routine

Electronic System Diagnosis and Repair• It is important to be clear about two definitions:

• Symptom(s) – what the user of the system (vehicle) notices• Fault – the error in the system that causes the symptom(s)

Symptom The effect of a fault noticed by the driver or technicianFault The cause of the symptom/problemRoot cause This may be the same as the fault, but in some cases it can

be the cause of itDiagnostics The process of tracing a fault by means of its symptoms,

applying knowledge and analysing test resultsKnowledge The understanding of a system that is required to diagnose

faultsLogical procedure A step-by-step method used to ensure nothing is missedConcern, cause, correction

A reminder of the process starting from what the driver reports, to the correction of the problem

Report A standard format for the presentation of results

Diagnostic terminology [4]

General Six Step Approach for Diagnostics [1] (Bonnick)• An organised and common-sense approach to problem solving is given

below [1]:1. Collect evidence. 2. Analyse evidence. 3. Locate the fault. 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.

• Certain steps can be recursive and it may be necessary to refer back to previous steps as one proceeds to a solution• Refer to the notes and [1] for more details of each step

General Six Step Approach for Diagnostics - Example• Consider the case of a vehicle with an engine that fails to start. The six

steps could be:

• Notice that the tasks in each step require an understanding of the system. Also notice the cause (root cause) and the fault are different in this example

Step Task(s)1 Is it a flat battery? Has it got fuel, etc.?2 If it appears to be a flat battery, what checks can be applied, e.g. switch on the headlamps.3 Assume that it is a flat battery.4 What caused the battery to become discharged?5 Assume, in this case, that the side and tail lights had been left on. So, in this case, recharging

the battery would probably cure the fault.6 Testing the system would, in this case, probably amount to ensuring that the vehicle started

promptly with the recharged battery. However, further checks might be applied to ensure that there was not some permanent current drain from the battery.

Alternative Six Step Approach [2],[4] (Denton Method)• An alternative (similar) routine for

diagnostics is illustrated on the right.• Steps 3 and 4 form a loop within

the larger loop until the fault is located. Using a logical method saves time and effort

1. Verify Check the fault

is as described

2. Collect Get more

information

3. Evaluate Stop and think

logically

4. Test Measure and

compare

5. Rectify Fix the fault,

replace the part

6. Check Make sure

other systems still work

Six-stage diagnostic process

Six Steps and Three C’s• The six steps form the three C’s (concern, cause, correction) in the

automotive repairs and diagnostics process. Their relationship is shown below:

Six-stage process CCCVerify ConcernCollect

CauseEvaluateTestRectify CorrectionCheck

Six-stage process and CCC comparison

Alternative Six Step Approach [2],[4] (Denton Method) - Example• After connecting a hosepipe to the tap and turning on the tap, no water comes

out of the end. Your knowledge of this system tells you that water should come out providing the tap is on. The following stages of the diagnostic process are required:

Step Task(s)1 Confirm that no water is coming out by looking down the end of the pipe.2 Does water come out of the other taps, or did it come out of this tap before you

connected the hose?3 Consider what this information tells you, for example, the hose must be blocked or

kinked.4 Walk the length of the pipe looking for a kink.5 Straighten out the hose.6 Check that water now comes out and that no other problems have been created.

Alternative Six Step Approach [2],[4] (Denton Method) – Student Activity 2• After turning on my computer the screen is blank. Use your

knowledge of computers to complete the stages of the diagnostic process:

Step Task(s)123456

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Alternative Six Step Approach [2],[4] (Denton Method) – Student Activity 3

• In the notes, Figure 3 illustrates an eight-step diagnostic procedure for vehicle systems [3]• In groups, rearrange/classify these 8 steps into the six step general

diagnostic process.

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Electronic System Diagnosis and Repair• You will learn how to diagnose various vehicle electronic systems later

on in the semester (weeks 9-13)• You will learn about the scope and of the rectification (repair) process

in the last weeks of the semester

References• [1] A. W. M. Bonnick, Vehicle Electronic Systems and Fault Diagnosis A

Practical Guide for Vehicle Technicians. NY: Routledge, 2013. (ebook in Unitec library)• [2] T. Denton, Automobile Electrical and Electronic Systems: automotive

technology: vehicle maintenance and repair. NY: Routledge, 2012. (available in Unitec library)• [3] J. D. Halderman, Diagnosis and Troubleshooting of Automotive Electrical,

Electronic, and Computer Systems. NJ: Pearson, 2012. (available in Unitec library)• [4] T. Denton, Advanced Automotive Fault Diagnosis: automotive

technology: vehicle maintenance and repair. NY: Routledge, 2012.