AUR30405
CERTIFICATE III IN
AUTOMOTIVE
MECHANICAL
TECHNOLOGY
AURT366108A
Carry out diagnostic procedures
LEARNER WORKBOOK
© Commonwealth of Australia 2011
ISBN: 978-1-876838-24-9
This document is available under a “Free for Education” licence for educational purposes – see
http://www.aesharenet.com.au/FfE2 for details.
This work is copyright. You may download, display, print and reproduce this material in whole or in part or in
modified form (retaining this notice) for your personal, non-commercial use or use within your organisation.
If you use, display, or reproduce this material or a modified form of it in whole or in part within your
organisation you must include the following words in a prominent location within the material in font not less
than size 12: ‘The views expressed in this publication do not necessarily represent the view of the Minister
for Education or the Australian Government. The Australian Government does not give any warranty nor
accept any liability in relation to the contents of this work’. Apart from any use as permitted under the
Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights
should be addressed to the Commonwealth Copyright Administration, Attorney General’s Department,
Robert Garran Offices, National Circuit, Barton ACT 2600 or posted at http://www.ag.gov.au/cca.
Funded under the Workplace English Language and Literacy (WELL) Program by the Australian Government
Department of Education, Employment and Workplace Relations.
The views expressed in this publication do not necessarily represent the view of the Minister for Education or
the Australian Government. The Australian Government does not give any warranty nor accept any liability in
relation to the contents of this work.
1
AURT366108A Carry out diagnostic procedures
1
Elements: ........................................................................................................... 1
About the workbook ....................................................................................... 1
Assessment ........................................................................................................ 3
Skills Recognition .............................................................................................. 4
Access and equity .......................................................................................... 4
Introduction
5
What is ‘diagnosis’? ........................................................................................ 5
What is ‘normal’ and ‘abnormal’? .............................................................. 6
What is a diagnostic procedure? ................................................................. 6
Safety ................................................................................................................. 7
Tasks and hazards............................................................................................ 8
Activity 1 ........................................................................................................ 9
Carrying out automotive diagnosis
11
The importance of diagnosis ....................................................................... 11
Symptoms, faults and causes ...................................................................... 13
Activity 2 ...................................................................................................... 17
The steps in a diagnostic procedure ......................................................... 22
Gathering information for diagnosis .......................................................... 23
Types of diagnostic procedures ................................................................. 24
Activity 3 ...................................................................................................... 27
Six-step diagnostic procedure
29
Apply six-step diagnosis to a real problem............................................... 32
Activity 4 ...................................................................................................... 37
Activity 5 ...................................................................................................... 41
Reporting and documenting diagnosis and repairs
43
Why do we need to document the diagnostic process? ..................... 43
Activity 6 ...................................................................................................... 49
Writing a diagnostic report .......................................................................... 53
Parts of a Report ............................................................................................ 54
Activity 7 ...................................................................................................... 57
Other diagnostic approaches
59
Branching diagnostic procedures.............................................................. 59
Activity 8 ...................................................................................................... 61
‘Black Box’ Diagnosis .................................................................................... 63
On-Board Diagnostics ................................................................................... 65
Reading codes and information with a scan tool .................................. 68
Proprietary and generic scan tools............................................................ 69
What information is available from an OBD system? ............................. 70
Activity 9 ...................................................................................................... 75
Activity 10 .................................................................................................... 79
Glossary
81
1
AURT366108A Carry out diagnostic
procedures
This unit covers the competence required to diagnose component/equipment faults from different
symptoms and to nominate repair action.
Elements:
1.
Prepare to diagnose faults
2.
Apply technology to isolate fault(s)
3.
Recommend rectification method(s)
4.
Component/equipment is prepared for customer use
About the workbook
This workbook is designed to assist you in gaining underpinning knowledge and developing practical
skills to achieve the competency standard AURT366108A Carry out diagnostic procedures within the
context of light vehicles.
This workbook contains:

information

questions

practical activities

directions to use additional resources.
The workbook is divided into stages. At the end of a stage, you will see an icon (picture with a
meaning) asking you to check your answers and/or practical activities with your trainer. This helps
the trainer to monitor your progress.
© Commonwealth of Australia 2011
1
What do the icons mean?
An icon is a picture with a meaning. In the workbook, these icons tell you something about:

what to do next (activity, check your answers, watch a video clip) or

the text (this is a safety warning).
Complete an activity
Check your answers with your trainer
Watch this video clip
Safety warning
2
© Commonwealth of Australia 2011
3
Assessment
To meet the assessment requirements for this competency standard you must demonstrate the
following:
Knowledge of:

OH&S regulations/requirements, equipment, material and personal safety requirements

diagnostic procedures and problem-solving techniques

symptom and cause differentiation

work organisation and planning processes

enterprise quality procedures

document responsibilities

document procedures.
Practical ability to:

Develop a diagnosis strategy to determine a fault

Carry out systematic diagnosis to test for a range of faults, using meters/ gauges/
measuring equipment

Interpret test results and identify the actual fault/s

Recommend rectification method/s.

Report findings in approved workplace format
© Commonwealth of Australia 2011
3
Skills Recognition
You may already have knowledge and skills for all (or part) of this competency standard. If you
believe you can demonstrate that you already have the skills and knowledge required, talk to your
trainer about applying for Skills Recognition.
This is also known as Recognition of Prior Learning (RPL), Recognition of Current competence (RCC),
or simply Recognition.
Skills Recognition is a process for gaining credit for those skills and knowledge gained through work
experience, formal training or other life experience.
Access and equity
In training, access and equity means ensuring that people with differing needs and abilities have the
same opportunities to successfully gain skills, knowledge and experience through education and
training. It is about removing barriers and providing the supports people need to access, participate
and achieve, irrespective of their age, disability, colour, race, gender, religion, sexuality, family
responsibilities or location.
For students with disabilities, training organisations may make adjustments to ensure equal
opportunity. Reasonable adjustments are designed to minimise the disadvantage experienced by
learners with a disability and can include administrative, physical or procedural modifications.
NOTE:
If you believe you could benefit from support to help
you overcome a barrier to participation, you should
speak to your trainer or the person in your RTO
responsible for access and equity.
4
© Commonwealth of Australia 2011
5
Introduction
This workbook assumes that you have already achieved competence in all the other vehicle systems
you need for your work.
The workbook will help you to develop skills in applying your technical knowledge in a systematic
way to diagnose faults in vehicles or other machinery.
The workbook uses the term ‘vehicle’ but all the processes and procedures can also be applied to
other machines or pieces of equipment.
What is ‘diagnosis’?
Motor vehicles (or machines or other equipment) sometimes break down. They develop faults or
problems, and repair technicians (that’s you) need the knowledge and skills to:

find the cause of the fault, and

fix it.
The first step is called ‘fault diagnosis’.
How do you do it?
Guessing is not good enough - you need to make a systematic, logical series of checks to identify
the fault. You need:

a sound knowledge of the principles and operation of the system or component being
checked

to be able to recognise whether a component is working normally or not

to think carefully about all the things that could cause a particular fault

to test each possible cause to identify (or diagnose) the actual problem.
Diagnosis is the process of identifying a fault, determining its cause and selecting possible solutions.
Sometimes it is called ‘trouble shooting’ or ‘fault finding’.
© Commonwealth of Australia 2011
5
What is ‘normal’ and ‘abnormal’?
Everything in a vehicle is in either a ‘normal state’ or an ‘abnormal state’.
Normal means things are okay; they are the way they should be.
Abnormal means things are NOT okay, or NOT the way they should be.
We can say that either ... the steering is working normally, or it is not.
... the alternator is charging normally, or it is not.
... the handbrake is working normally, or it is not.
We can also talk about ‘normal events’ and ‘abnormal events’.
An event is something that happens.
An event occurs when a gear is selected, or a turn signal lights up, or the cooling fan turns on.
A normal event is when something happens in exactly the way it should.
An abnormal event is when something happens NOT in the way it should.
For example, the engine misses, the steering loses power assistance, or a rod comes out through
the side of the engine block.
The purpose of all motor vehicle diagnosis is:

to recognise abnormal states and abnormal events

to find the cause of those abnormal things, and

to recommend repairs which will return the vehicle to its normal state of operation.
What is a diagnostic procedure?
A procedure is a logical set of steps to follow. Using a logical procedure will help you to diagnose a
vehicle’s problem quickly and efficiently. All diagnostic techniques are based on logical thinking and
a systematic approach to solving the problem. They often take the form of a diagram or flow chart.
You might find diagnostic procedures in the vehicle manufacturer’s workshop manual, or you might
make one up yourself based on your knowledge and experience.
This workbook explains how to use and develop diagnostic procedures.
6
© Commonwealth of Australia 2011
7
Safety
All diagnostic procedures must be carried out safely. Working safely helps prevent injury to
yourself and others. It also prevents damage to the vehicle or test equipment.
Today’s sophisticated vehicle systems (such as electronic systems for engine, transmission
and body management; anti-lock brakes and vehicle stability control) can easily be damaged
by unsafe or careless test and repair procedures.
Any damage or injury in the workplace can be very costly – look at some of the costs in the table
below.
Damage or injury
Costs
Injury to a worker





pain, possible disablement
medical costs
loss of income
government safety inspections
increased workplace insurance premiums
Damage to a vehicle



cost to the workshop
reduced profits
damaged reputation
Make sure you follow all:

Occupational Health and Safety (OHS) guidelines

safety instructions from your employer

vehicle or system safety precautions given by the vehicle
manufacturer.
ALWAYS wear suitable Personal Protective Equipment (PPE).
Minimum PPE requirements are:

glasses or mask to protect eyes from flying particles and liquid
sprays

gloves for handling hot items and chemicals

suitable neat-fitting overalls or clothing

safety footwear.
Some jobs will require specialised equipment, such as a respirator.
Any supplied PPE must be used when a job requires it.
THINK SAFETY at all times
© Commonwealth of Australia 2011
7
Tasks and hazards
Here are some of the risks and hazards you may be exposed to when doing diagnosis and repair
tasks:
Hazard
Advice
Fire
Watch out for fuel leaks when working on fuel systems.
Eliminate anything which could start a fire.
Keep a fire extinguisher nearby.
Lifting
Never lift more than you can manage.
Ask for help, or use lifting equipment.
Exhaust Gases
Running engines need good ventilation.
Carbon monoxide (CO) in the exhaust can kill you.
Other exhaust chemicals can cause asthma and cancer.
Running
Engines
Don’t wear loose clothing when working around a running engine.
You could be dragged into drive belts or other moving parts.
Electric Shock
Ignition systems produce voltages of 30,000 to 50,000 volts.
Reaction to an accidental shock can throw you into contact with
moving parts such as the fan or drive belts.
Batteries
Batteries contain sulphuric acid (H2SO4).
Battery acid will destroy clothing, burn skin, and can cause
blindness if it gets in your eyes.
Batteries also generate explosive hydrogen gas (H2) when
charging, so keep sparks away.
Figure 1: Be careful with battery acid
8
© Commonwealth of Australia 2011
9
Activity 1
Tick the correct answer/s. There may be more than one correct answer.
Question 1
The term ‘diagnosis’ means:

Using a scan tool to extract codes

Using a logical process to solve problems

Repairing faulty components

Replacing faulty components.
Question 2
When a vehicle component or system is working the way it should be, we say that it is in:

A normal state

An abnormal state

A paranormal state

A sub-normal state.
Question 3
An automatic transmission, on up-shift, always makes a 2nd to 4th change and never selects 3rd. Is
this:

A normal event?

An abnormal event?

A paranormal event?

A sub-normal event?
© Commonwealth of Australia 2011
9
Question 4
Personal Protective Equipment (PPE) for technicians working in an automotive workshop should
include:

Eye protection- glasses or face mask

Gloves to protect hands from burns and chemicals

Skin protection- overalls or suitable protective clothing

Over-lapping steel abdominal protection when balancing wheels

Safety footwear.
Question 5
Working around any of the vehicle systems listed below can be dangerous. Describe (write down)
some possible dangers associated with each system:
Fuel system _____________________________________________________________________
________________________________________________________________________________
Ignition system ___________________________________________________________________
________________________________________________________________________________
Batteries ________________________________________________________________________
________________________________________________________________________________
Running engines __________________________________________________________________
________________________________________________________________________________
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
10
Date: .....................
© Commonwealth of Australia 2011
1
1
Carrying out automotive diagnosis
The importance of diagnosis
Diagnosis is an extremely important task in today’s workshop.
Fast, accurate diagnosis can save money for both the customer and the workshop.
The table below shows some of the benefits of good diagnosis for the three stakeholders in
automotive repair.
Who?
Benefits
The customer



Time and money has not been wasted on inefficient diagnosis methods
Their vehicle is off the road for the minimum amount of time

Skilled and efficient employees are valued and rewarded by their
employer
They have the satisfaction of doing a good job
The technician

The workshop


No re-work required through wrong diagnosis
The job is completed in the shortest possible time, and productivity
(time spent per job) is improved so more jobs can be completed in a
day
Warranty costs are down because the work is high-quality
Bad or careless diagnosis can have just the opposite effect.
Not systematic.
Takes longer to carry
out & costs more
A very unhappy customer!
Decides to take her/his
vehicle somewhere else in
the future
Might be the wrong
diagnosis and the
wrong repair
Results in a ‘re-work’
Costs the workshop
even more in wasted
time
Figure 2: The result of bad diagnosis
© Commonwealth of Australia 2011
11
Which technician would you choose?
I bought this van second hand not long
ago– it’s a rear wheel drive. When I
accelerate, there’s a loud grinding and
groaning noise, and also a bit of vibration.
What could it be?
Technician 1 - Guessing
Technician 2 - Logical diagnostic procedure
Joe Goodenough took the van for a quick test run.
Jack Getitryte carried out a few more tests and collected more information,
including looking in the workshop manual.
The noise seems to be coming from the manual
transmission. It’s an old vehicle, so the
transmission bearings are probably faulty.
I think the transmission needs rebuilding.
The manual says that one reason for noise and
vibration on acceleration can be incorrect driveline
angles. I’ll check to see if that could be the problem.
Joe didn’t do any more checks.
Jack checked and found that the rear axle shims or wedges (which set the drive
line angle) were missing, left out after a previous repair.
A rebuilt transmission was fitted and road tested.
The shims were replaced and the problem was cured!
The noise was exactly the same as before!
12
© Commonwealth of Australia 2011
13
Symptoms, faults and causes
Understanding the language
When we diagnose a problem, we look at the symptoms of the fault and try to find the cause of
them. What do these words mean?
Symptom
A symptom is a clue that something is wrong.
It is a noticeable change - we might see, hear, smell or feel something different.
The clutch
feels funny...
The engine
cuts out!
These are both symptoms of a problem. The owner or driver recognises them as abnormal. They
won’t know what the fault is, but will know that something about the car is different.
A problem or fault in a vehicle is usually first noticed by the regular driver of the vehicle, because
they are most familiar with the way it normally operates, and spend a lot of time behind the wheel.
It is the technician’s job to look at the symptom and work out what fault has caused it.
In fifth gear, the engine
revs hard but the car
won’t accelerate
normally.
The front tyres
have worn out
very quickly.
The engine stopped
suddenly, and it won’t
re-start.
These symptoms are the abnormal things that the driver has noticed about the performance of
her/his vehicle. They all point to some problem which has produced the symptom.
© Commonwealth of Australia 2011
Fault
A fault is an abnormal condition in a system or component. Something has gone wrong which we
need to identify and repair.
Faults may be:
Hardware faults - Physical faults that we can observe or measure, such as parts which are
broken, worn, out-of-specification, damaged, incorrectly adjusted or assembled.
Software faults - May not be directly observable, such as faulty, incorrect or corrupted
programs in electronic modules.
The fault may be one or more of the following things:
Type of fault
Example
Not working at all


A blown headlight globe
A failed open circuit fuel injector
Working, but not the way it
was designed to work


Working headlights which are badly aimed
A fuel injector with a faulty spray pattern
Doing something it is not
supposed to do


A headlight that won’t turn off
A fuel injector with a constant leak
Making something undesirable
happen


Causing the headlight fuse to blow
Generating excessive exhaust emissions.
Here are some examples of symptoms reported and the faults which were found to match them:
Symptom
Fault
In fifth gear, engine revs hard but car won’t
accelerate
Slipping clutch
Excessive tyre wear
Incorrect wheel alignment
Engine stopped suddenly, won’t re-start
Broken cam belt, bent valves
These faults can be repaired by replacement of parts, or by adjustment.
But what caused those faults?
There are many reasons why a clutch might slip, but if we simply fit a new clutch kit without
discovering the underlying cause of the slippage, that vehicle might return to the workshop on the
back of a tow-truck!
14
© Commonwealth of Australia 2011
15
Cause
A symptom might indicate a fault in a customer’s vehicle, and a faulty (worn, broken) component
might be found, but what produced that fault?
Something must have caused that change.
Finding the cause of the faults will allow the technician to choose the right repair to correct the
fault, and prevent any re-work under warranty (‘come backs’).
Example:
Result
That car will eventually
come back with
exactly the same
symptom!
Symptom
Instrument panel oil
light is on when the
engine is running
Cause
Technician didn’t
find the cause of
the low oil level
Fault
Engine oil
level is low
Action
Technician tops up the oil, checks
that the oil light is now off, and
returns the car to the customer
Figure 3: the importance of finding the cause
Remember those symptoms and faults shown in the table above?
Here are the some possible causes of those faults:
Symptom
Fault
Cause
In fifth gear, engine revs hard
but car won’t accelerate
Slipping clutch
Clutch driven plate worn out after
200,000km of service. Normal wear.
Excessive tyre wear
Incorrect wheel
alignment
Bent steering arm - impact with road
gutter
Engine stopped suddenly,
won’t re-start
Broken cam belt, bent
valves
Belt overdue for replacement.
Leaking camshaft oil seal.
© Commonwealth of Australia 2011
This page has been left blank intentionally.
16
© Commonwealth of Australia 2011
17
Activity 2
Tick the correct answer/s. There may be more than one correct answer.
Question 1
Accurate diagnosis is important because:

It can save the customer money

It can reduce workshop costs

It keeps customers happy with your work

It reduces the chance of having to do the job again.
Question 2
When diagnosis is quick, efficient and accurate:

Workshop productivity is improved

The technician’s skills are demonstrated and valued

The workshop can close early for the day

The customer gets his/her vehicle back in reasonable time at affordable cost.
Question 3
A symptom is:

A piece of equipment

Someone who has knowledge

A noticeable change

No change in operation.
© Commonwealth of Australia 2011
Question 4
Symptoms can be recognised because they:

Make vehicles perform normally

Change how something performs

Are imagined by the owner

Are a noticeable change in performance.
Question 5
A symptom is:

A sign that something is operating

An unnoticeable change in a vehicle’s operation

The failure of some component or system

A perceptible change in a vehicle’s operation.
Question 6
A fault is a component or system which is:

Not working at all

Not there at all

Not doing what it is supposed to be doing

Worn, broken or out of adjustment.
Question 7
A cause is:
18

When the vehicle fails completely

When only part of a system is working

The reason why a fault occurs

An abnormal state in a component or system.
© Commonwealth of Australia 2011
19
Question 10
Here are three statements about a vehicle with a problem.
Which is the symptom, fault, and cause?
Draw lines to match each statement with the correct box.
SYMPTOM
Sticking caliper slides on
right front caliper
SYMPTOM
FAULT
Noise and extreme heat
coming from right wheel
CAUSE
Poor or lack of vehicle
servicing
Question 11
Describe a simple problem that you have come across at work recently.
Write down the symptom, fault and cause of the problem. You may also explain your answer to
your teacher.
SYMPTOM
FAULT
CAUSE
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
© Commonwealth of Australia 2011
Date: .....................
This page has been left blank intentionally.
20
© Commonwealth of Australia 2011
21
Diagnosing is not guessing
Non-technical people see a symptom and guess at the cause.
But a technician doesn’t guess – they start to thing logically about what the cause of the fault could
be.
One of my car’s parking
lights isn’t working. The
globe must be blown.
Well, the globe isn’t working,
but I wonder why it’s not
working? What has caused it?
I know that the globe is part of the lighting system, which is part of the
electrical system. What are the most likely things which could cause this
symptom of ‘light not working’?






Blown globe?
Blown fuse?
No supply voltage?
Not switched on?
Switching circuit fault?
Open circuit wiring harness?


Corroded connections?
Supply voltage too high - blown
globe?



Body Control Module fault?
Vibration - blown globe?
and possibly more.
If you want to find the cause which led to the fault and the symptom, you need to:

Gather more information about the complaint

Gather more information about the systems involved

Carry out a variety of tests

Think about (analyse) your information and test results; and

Confirm the cause of the problem.
Only then can you decide what repair is needed, and afterwards confirm that the fault and its cause
have been eliminated.
© Commonwealth of Australia 2011
The steps in a diagnostic procedure
The diagnostic procedure you should use in the auto repair industry is similar to what a doctor does
when you walk into the surgery with a minor illness.
Diagnostic step
What the doctor does
Gather more
information about the
problem

Asks what your symptoms are (cough/cold/dizziness/pain in
the leg/head ...)
Gather more
information about the
systems involved

Asks questions -how long have you had the cough/cold?
What sort of cough is it? Can you show me? Where is the
pain? How bad is it?
Checks your past medical history in her records.

Carry out a variety of
tests using test
equipment


Uses a stethoscope to listen to the cough, measures blood
pressure or temperature, probes or manipulates the painful
area, x-ray etc
Might also consult some other source of medical information
eg books, internet, colleagues
Think about (analyse)
the information and test
results and reach a
diagnosis


Decide on the “repair”

Prescribes the treatment for your condition eg
medication/physiotherapy/brain transplant etc
Confirm the cause of the
problem.

Asks you to come back for a check-up to make sure the
problem is fixed

Considers all the information gathered, including test results
Compares this with her expert medical knowledge of the
human body
Works out the cause of your problem
Your doctor follows a logical diagnostic procedure. She is able to treat you successfully because:

She has a very good understanding of the system in which the problem exists.

She applies a logical, systematic procedure to working out what the cause of the
problem was.
You need to be able to do exactly the same to successfully diagnose vehicle faults!
22
© Commonwealth of Australia 2011
23
Gathering information for diagnosis
Following a procedure (a set of steps) is nothing new to automotive repair technicians. When you
change a wheel on a vehicle you follow a procedure to make sure it is changed safely and refitted
securely.
This procedure might be developed by the vehicle manufacturer or you can create your own
procedures to follow. Sometimes you might combine these for a particular job.
Your knowledge
Your diagnostic ability depends on a good knowledge and understanding of the system in which the
problem exists. But you can’t know everything! Most technicians become very familiar with
particular systems (engine management, for example) on a limited range of vehicles.
When you find that you don’t know enough about a vehicle system, where can you look for help?
Use other sources of information
Gathering information is part of the diagnosis process and is often easily available.
Some of the reliable sources you could use are:

Other technicians in the workshop

Workshop manuals, and manufacturer’s technical hot-lines

Service bulletins from the manufacturer

Service information from industry and commercial associations e.g. AACC, IAME,
Autotech.
Keep up-to-date
As a professional, you should take every opportunity
to improve your knowledge.
Don’t leave it until you’re in the middle of a diagnosis
job!
Keep your knowledge up to date through:

Workplace training

TAFE courses

trade association courses

technical journals (publications)

workshop manuals.
© Commonwealth of Australia 2011
Internet InformationNever believe information you
find on the Internet unless you
are absolutely certain that it
comes from either an official
factory site, or is otherwise
totally reliable.
Never trust anything you read on
sites such as the one-make
forums- they are usually full of
misinformation and myths.
Types of diagnostic procedures
There are lots of different procedures for diagnosis of vehicle faults, but they are all logical and
systematic. This workbook will deal with:

Step-by-step procedures

Branching procedures

‘Black box’ procedures.
Often a diagnostic procedure can be shown on a diagram. In the medical example described earlier,
the doctor followed this step-by-step process:
Figure 4: Step-by-step procedure
This could be used as a general procedure to follow on other diagnosis tasks.
Often you can make a few small adjustments to suit the particular job.
24
© Commonwealth of Australia 2011
25
Feedback Loops
Here is another, slightly different, diagnostic chart. It has a “feedback loop” which prompts you to
re-test or do further tests if you don’t find the fault on the first attempt.
Step 1
Verify fault exists
Step 2
Gather information
Step 3
Carry out tests
Fault not found
Step 4
Consider the
information
Step 5
Identify and repair
the fault
Step 6
Check to make sure
Figure 5: Feedback loop
You can see that both of these diagnostic procedure flow charts are quite similar.
You could apply these procedures to many straightforward diagnosis jobs.
An easy diagnosis
A customer traded in his old car on a new one. A month or two later he returned to
the dealership complaining that recently, when he had to make an emergency stop,
there was “a groaning noise and the brake pedal felt funny”.
When he demonstrated this to the technician it was clear that he had simply felt the
normal operation of the anti-lock braking system in his new car which he had never
experienced before. He was very pleased to be told that there was no problem, and
to be given instructions on the correct way to use ABS in an emergency.
However, most diagnosis isn’t that simple.
However,
© Commonwealth of Australia 2011
This page has been left blank intentionally.
26
© Commonwealth of Australia 2011
27
Activity 3
Tick the correct answer/s. There may be more than one correct answer.
Question 1
Which of these things are essential steps in any diagnostic procedure?

Carrying out tests

Analysing information

Substituting parts

Gathering information.
Question 2
Write the 6 actions on the left into the boxes.
Put them in the best order to show a simple diagnostic procedure.
Consider the information
Repair the fault
1.
2.
Carry out more tests if needed
3.
Verify that the fault exists
4.
Check the fault is fixed
5.
Gather information
6.
© Commonwealth of Australia 2011
Question 3
When diagnosing vehicle faults, it is important to keep up with the latest information. What are
some ways you could increase your knowledge of the systems you work on?
List them below.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
Question 4
A ‘feedback loop’ in a diagnostic procedure can:

Cause an abnormal noise in the audio system

Take you out of the procedure and direct you to another job

Prompt you to re-test, or make extra tests

Give advice on how to arrange the wiring loom.
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
Date: ....................
.
28
© Commonwealth of Australia 2011
Six-step diagnostic procedure
Let’s look at each of those six steps in more detail.
1. Confirm the symptom
Make sure that the customer’s concern is valid (true).
Try to reproduce the symptoms described by the customer or have the customer demonstrate the symptom
to you. If you do a road test- make sure it is done in a safe manner!
2. Gather information
A. Question the customer closely about their concern. Once they leave the workshop you won’t have easy
access to them.
“When did you first notice the problem? What conditions was the vehicle operating under at the time? High
load? Light load? In traffic? Cruising on the freeway? How long since the engine was started? What repairs or
service have been done recently?”
B. Try the “look and feel” test, if the problem allows it. Carefully inspect suspect areas, looking for obvious
leaks, breaks, stains, noises, loose or damaged wiring etc.
C. Use other information sources:






Your workplace colleagues- have any of them come across these symptoms before?
On-board diagnostic trouble codes (more about this later)
Service bulletins relevant to that vehicle to see if it is a known problem or subject to a recall
Workshop manuals have trouble-shooting guides
Trade associations have technical information lines for advice and/or vehicle specifications eg the
australian automobile chamber of commerce (aacc), or the institute of automotive mechanical engineers
(iame)
Commercial data suppliers- companies who sell automotive technical and repair information in book or
digital form.
SOME HINTS:
Gather as much information as possible at the beginning of the job.
Never overlook the obvious.
Look for simple solutions first, before pulling the car to pieces.
Never assume anything. Always check it yourself.
29
© Commonwealth of Australia 2011
3. Consider the information
and evidence gathered
What you have learned from your investigation and any tests you have carried out so far?
What things are not possible faults, based on the evidence?
What things could be causing the problem?
At this stage you have eliminated most of the possibilities, and have strong suspicions about one or two
others. You may need to do some more tests, or partially dismantle a system, to finally identify the fault.
Example: The complaint is “overheating all the time”, and you have found that the vehicle recently had the
head gasket replaced. You would probably do some more tests to see if a failure of that repair was causing
the symptoms.
4. Locate the fault and its
cause
If all has gone well you will now be able to confidently identify the faulty component or system.
4A. Feedback loop
What caused the rust build-up?
Example: The engine is overheating, and the fault is “the cooling system passages are blocked with rust”.
You suspect that the coolant and corrosion inhibitor is old, worn out, or at the wrong concentration.
A further test of the coolant should confirm this. You now know what the fault is, and what caused the fault.
5. Repair the fault and its
cause
Decide on the most suitable repair to eliminate the fault.
Example: Thorough flushing and cleaning of the entire system, including blocked passages, replacement as
required of welsh plugs and any other consumable items like hoses, and filling with new coolant.
In other cases there might be several equally valid alternatives.
Example: Overhaul the starter motor
OR fit a reconditioned change-over unit
OR fit a brand-new replacement.
Your choice might be influenced by such things as cost, time, complexity, or workplace policies.
6. Check all systems and
confirm fault is fixed.
Check all related systems, as well as the faulty one, to confirm that:
the original symptoms are no longer present under any operating conditions, and
no other faults have been introduced.
30
© Commonwealth of Australia 2011
Step 2 c) Gather information - Use other information sources
Here is an example of the sort of information a workshop manual might provide:
31
Symptom
Possible Fault
Engine overheats







Loss of coolant
Belt tension incorrect
Radiator fins obstructed
Thermostat stuck closed
Cooling system passages blocked by rust, scale or other foreign material
Water pump not working- impeller loose, eroded
Thermo fan not working
© Commonwealth of Australia 2011
Apply six-step diagnosis to a real problem
Let’s apply this process to a diagnostic job mentioned earlier in this workbook - the parking light not working.
Step 1
Confirm the
symptom
Step 2



Asked the customer to point out the light which is not working
Confirm that it is the left front parking lamp, and only the left front, which is not working
The symptom is real - move on to Step 2.
a. Question the car’s owner about the park light’s use and behaviour up to the time of noticing the fault. Some sample
questions and answers are in the table below this one.
Gather information
b. Do the “look and feel” test. You find:





The park light is mounted firmly in the plastic front bumper.
The panel fit is good.
The bumper is not loose.
Looking behind the lamp, we can see that the wiring loom is intact and securely clipped to the bumper.
We remove the globe and inspect it - sure enough, it’s blown!
But what causes globes to blow?
32
© Commonwealth of Australia 2011
Step 2
c. Use other information sources:
Gather information
– cont.
Even though we reckon we know this stuff, let’s check the workshop manual for any further information. The manual
provides this chart:
Symptom
Cause
Globe blown
Old age - very high number of on-off cycles
Vibration – loose lamp holder, loose panel mounting very
rough roads
Loose electrical connections – number of rapid on-off cycles
High circuit voltage – over stressed filament
Manufacturing defect
Now that we have some reliable information, we can move on to Step 3.
Step 3
What have we learned from our investigation so far?
Consider the
information and
evidence gathered
Have we got enough information and evidence?
Can we confidently say what caused the globe to blow? Or can we at least narrow down the possibilities?
Let’s compare each of the possible causes from the workshop manual with the evidence and judge how likely each
possible fault is.
33
© Commonwealth of Australia 2011
Feedback loop
Test 1 - We need more information. Time to get the multimeter out!
Starting the engine and turning on the park light, we back-probe the wiring connector at the faulty lamp with our
multimeter set on the 20 volt range.
The result: 15.1 volts supplied to the light. Is this the right voltage?
Only one way to tell - look it up in the workshop manual! The lighting circuit is part of the electrical circuit. The electrical
circuit is supplied by the alternator.
According to the workshop manual - Alternator regulated output voltage = 14.0 – 14.2 volts
Compare the measured circuit voltage with the manufacturer’s specifications - it’s nearly a volt too high!
We can now say that the most likely cause of the blown globe is high circuit voltage, which over-stressed the globe’s
filament, causing early failure.
Test 2 - We need to test the battery to make sure it hasn’t been damaged by over charging. Luckily it’s OK.
Step 4
We now know the fault is a blown globe, and its cause is high circuit voltage which over-stressed the globe’s filament.
Locate the fault
and its cause
34
© Commonwealth of Australia 2011
Step 5
The blown globe must be replaced with a new one.
Repair the fault
and its cause
The circuit voltage must be reduced to manufacturer’s specifications. Alternator output voltage on this car is set by the
voltage regulator inside the alternator. The regulator needs to be replaced, but experience tells us that the alternator
brushes will have suffered some natural wear as well.
We could:



overhaul the alternator in our workshop
fit a change-over reconditioned unit supplied by the local auto electrician
fit a brand new unit supplied by the dealership.
Our recommended repair is to fit the reconditioned unit, which has been bench-tested and is guaranteed. It is equivalent
to the new unit, but is much cheaper. We won’t do the overhaul ourselves because our workshop is fully booked, and in
any case we can’t do the job any cheaper than the reconditioned unit.
We should also advise the customer that all of the vehicle’s light globes have been stressed by excessive circuit voltage.
In the interests of customer satisfaction, it would be wise to replace all of the safety-related globes to avoid any
subsequent “old-age/ stress related” failures in the near future.
Step 6.
Check all systems
and confirm fault is
fixed.
35
We test all functions of the lighting system for correct operation, switching, illumination etc.
Re-check alternator regulated voltage, following manufacturer’s procedures.
The job is complete, apart from the paperwork.
© Commonwealth of Australia 2011
Step 2 a. Gather information -Question the car’s owner
What questions could we ask this customer?
36
Questions
What information do we want?
Answer
How often do you use the park lights?
We want to judge how much service the light has
given prior to failure
About 2 hours each week
What sort of driving do you do?
We want to know if the car travels on rough
roads a lot
Mostly city driving-sealed roads
Has it ever stopped working before?
To see if we’re chasing a recurring fault
No
Have any other lights stopped working in the
past?
To get a history of the car’s lighting problems
Yes, a tail light and one headlight,
at different times
What did you do about those failures?
We want to know about any work done on the
lighting system prior to this
A friend put new globes in- he
said they were blown
Have you noticed anything else unusual about
the operation of your car’s lights recently?
We want to know if there have been any other
symptoms such as flickering, changes in
brightness etc
No
Has any other work been done on the front end
of the car recently?
This could point to problems created during an
unrelated repair, such as panel damage
No
© Commonwealth of Australia 2011
37
Activity 4
Question 1
A customer complains that his car’s engine “misses under load”.
What could you do to confirm that this symptom exists?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
Question 2
You need to get more information about the fault. Write down four useful diagnostic questions you
could ask the owner.
1. _____________________________________________________________________________
2. _____________________________________________________________________________
3. _____________________________________________________________________________
4. _____________________________________________________________________________
Question 3
Choose a workshop manual and look up the manufacturer’s trouble shooting information for the
symptom of “engine missing under load”.
OR choose a different symptom you would like to investigate.
Complete the table below by filling in the possible causes of this problem.
Symptom
Possible causes
© Commonwealth of Australia 2011
Question 4
The steps of a typical diagnostic procedure are set out below in boxes.
Explain the purpose and importance of each step.
1. Confirm the
symptom
Purpose _______________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
2. Gather
information
Purpose _______________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
3. Consider the
information and
evidence gathered
Purpose _______________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
4. Locate the fault
and its cause
Purpose _______________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
5. Repair the fault
and its cause
Purpose _______________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
6. Check all systems
and confirm fault
is fixed.
Purpose _______________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
38
© Commonwealth of Australia 2011
39
Question 5
Here are some questions you might ask a client to collect information about a vehicle problem.
Why would you ask each question? How could the customer’s answers help you to diagnose the
problem?
a) “How often does the problem happen?”
________________________________________________________________________________
________________________________________________________________________________
b) “How old is the vehicle?”
________________________________________________________________________________
________________________________________________________________________________
c)
“When does the problem occur?”
________________________________________________________________________________
________________________________________________________________________________
d)
“Have you had any work done on the vehicle recently?”
________________________________________________________________________________
________________________________________________________________________________
e)
“Do many different people drive the vehicle?”
________________________________________________________________________________
________________________________________________________________________________
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
© Commonwealth of Australia 2011
Date: .....................
This page has been left blank intentionally.
40
© Commonwealth of Australia 2011
41
Activity 5
Question 1
Create a diagnostic procedure for yourself in the space provided.
Include the six steps you have learned about.
Include all safety precautions necessary for safe work practices in your workplace.
You can design your procedure as a flow chart, or using dot-points, as long as another person could
easily follow your reasoning.
Remember to:

Ask questions and collect information

Think about all possible faults

Describe any tests you make

Recommend an appropriate repair.
The problem:
I’ve got a flat tyre!
© Commonwealth of Australia 2011
This page has been left blank intentionally.
42
© Commonwealth of Australia 2011
43
Reporting and documenting diagnosis and
repairs
Often in an automotive workshop you will need to write things down, record them, and pass them
on to other people.
This section deals with the documentation and reporting that may be required by diagnosis tasks.
Why do we need to document the diagnostic
process?
Recording information about a diagnostic procedure is important so that:

The technician can keep track of the process eg tests done and their results

The technician can see the build-up of information which will help them eventually
recognise the fault

The business can communicate accurately with the customer from the start of the
diagnostic procedure until the repair is completed and paid for

The business can obtain authority to repair at the appropriate stages as the procedure is
worked through

There is an accurate record if there is any dispute over the work done

There is a service record can be a helpful reference for future jobs.
The information should always be written down in an organised way so that anyone who looks at it
can understand it. It is risky and bad practice to rely on your memory – the information needs to be
written down, and not on a scrap of paper that can easily be lost or misplaced!
When a customer approaches a business for a fault to be diagnosed, most businesses set up a job
card for the particular job. The job card becomes part of the vehicle’s service record, which is a file
of information maintained by the workshop over time.
© Commonwealth of Australia 2011
Set up a Job Card
When a numbered Job Card or Repair Order is set up, you should record the following information:

Owner’s details

Car’s details

Customer’s concerns about the vehicle

Customer’s signature in the‘Authority to Repair’ space on the card.
The Authority to Repair is signed on the understanding that the customer will be consulted if the
repair is going to be bigger or more expensive than first thought.
Example:
STEADY EDDIE REPAIRS
Job No. 1234
Date: 29/06/2010
Service Adviser: L. Skywalker
Time: 08.45am
Technician:
A. Mechanic
Customer Name & Address:
Year/ Make/ Model
A. Person
2003 Daewoo Lanos
16 Long Street
1.5 2dr Manual White
Newburb VICTORIA 3999
VIN No: KLATF08YE3B12345xxx
Tel: 9123 4567
Engine No: A15SMS12345xxB
Customer Concern:
Kilometres: 165,732
Radio loses station tuning presets
Reg: ABC 123
Date & Time Promised:
Authority to Repair:
TBA
J Frost
Description of Work Carried Out
44
© Commonwealth of Australia 2011
45
Gather information
What questions would you (or another employee of the business) ask the customer?
Add this information onto the Job Card.
Car is seven years old.
Radio has been OK up until recently.
Once re-tuned it works fine, only loses pre-sets occasionally after engine starts.
What checks would you do?
A “look and feel” check - the radio is mounted firmly, and the connections are all secure.
After re-tuning the radio, repeated starting and stopping of the engine eventually causes the
symptom to re-appear. By this time the cranking speed is noticeably slower than it was earlier.
Add this information onto the Job Card.
Description of work carried out.
Visual inspection of radio & connections OK.
Re-tuned OK.
Carried out multiple engine start-stop, symptom returned (11th try).
Note - cranking speed getting slower.
Consider the information collected so far – what does it tell you?
The radio being made up of electronic components is a part of the electrical system, and so is the
starter motor – could the problems be connected?
Another test is needed to measure voltage drop at the battery during cranking.
© Commonwealth of Australia 2011
Feedback loop

Use a multimeter to measure voltage drop at the battery during cranking. Voltage drops
to 9 volts - it looks like the battery is faulty, and the low voltage is causing the radio to
lose its memory during cranking.

A specific gravity test of the electrolyte is good.

A battery capacity test shows that the battery capacity is now less than half what it was
when it was new, which accounts for the slower cranking speed.

A double-check of starter current draw (80A), using a good slave battery, shows that the
excessive voltage drop is not being caused by the starter circuit. Alternator output
measures 14.4 volts at 50 amps, which is within specifications.
Identify the fault and its cause
The technician is now confident that the faulty battery is the cause of the problem, and updates the
diagnosis record:
Add this information onto the Job Card.
Description of work carried out
Time on 09.35 am
Visual inspection of radio & connections OK.
Time off 10.10 am
Re-tuned OK.
Parts
Carried out multiple engine start-stop, symptom returned
(11th try).
Note - cranking speed getting slower.
Battery connections OK.
Spec Grav = 1.265
Cranking voltage = 9V.
Starter draw= 80A at 11 volts using slave battery.
Charging voltage 14.4V @ 50A.
Battery capacity 40%.
Battery is faulty
The technician has to stop here and clock off.
46
© Commonwealth of Australia 2011
47
Someone must contact the customer and tell them that a new battery is needed, to avoid any
misunderstanding later. The customer must agree to this repair, perhaps in writing.
Add this information onto the Job Card.
Authority to Repair
Additional Work - Authority to Repair
Repairs to radio
Fit new battery
Signature……J.
Frost
…
Signature …………...............…..
Date…29/06/10
Date:…29/06/10
OR via Telephone:
OR via Telephone:
Time received:…08.50 am
Time received: 10.30 am
Email:
Email:
Fax:
Fax:
Repair the fault and its cause
The technician can clock back on to the job and finish the repair:

Fit a new battery

Re-tune the radio to preferred stations.
Check all systems and confirm fault is fixed
Check all electrical systems for correct operation. The battery is put under load by turning on
headlights, heated rear screen, air conditioning etc and at the same time repeatedly operating the
starter motor.
The radio does not lose its pre-set tuning, confirming that the fault is fixed.
The last tasks for the technician are to:

Make sure that no dirty marks have been left anywhere on the car.

Park the car in the appropriate spot.

Return the driver’s seat to its original position, if it has been moved.
© Commonwealth of Australia 2011
Add this information onto the Job Card.
Description of work carried out
Time on 09.35 am
Visual inspection of radio & connections OK.
Time off 10.10 am
Re-tuned OK.
Carried out multiple engine start-stop, symptom returned
(11th try).
Time on 10.40 am
Time off 11.30 am
Note - cranking speed getting slower.
Battery connections OK.
Spec Grav = 1.265
Cranking voltage = 9V.
Starter draw = 80A at 11 volts using slave battery.
Charging voltage 14.4V @ 50A.
Battery capacity 40%.
Battery is faulty
Parts
N480ZZ battery
Repair
Fitted new battery
Re-tuned radio to customer’s stations
Tested for loss of pre-sets
System operation correct.
Then pass the Job Card on to Reception for processing.
Reception will:
48

prepare the invoice for the customer

inform them that the car is ready

carry out the hand-over when the customer arrives

explain any aspects of the repair as required

taking payment.
© Commonwealth of Australia 2011
49
Activity 6
Fill out the Job Card on the next page.
Use the information from the diagnosis task detailed in the section Applying these six diagnostic
steps to a real problem earlier in this workbook.
My parking light
isn’t working.
Find and use the VIN and engine numbers of any training vehicle in the workshop.
If a vehicle is not available, you can make these numbers up.
Make up the customer’s name and address.
© Commonwealth of Australia 2011
STEADY EDDIE REPAIRS
Job No. 1235
Date:…………….............…
Service Adviser: ………........………..................…..
Time: ………………............
Technician:
Customer Name & Address
…………………….........................…..
Year/ Make/ Model
……………………………………...….............................…
Reg. No. ………………………………….…………………….…
VIN No. ………………….…………….……………………….…
Tel:
Engine No. ………………..……………………………...….…
Customer Concern:
Kilometres …………….
Authority to Repair
Signature: .................... ………………
Date: …../….../.......
Date & Time Promised:
Description of Work Carried Out:
Time on
Parts
50
TBA
Time off
Cost
© Commonwealth of Australia 2011
51
Authority to Repair
Additional Work- Authority to Repair
………………………………………………..
………………………………………………..
Signature: .........................................………….
Signature: ……….................................….
Date: …../…./……..
Date: …../…./……..
OR via Telephone: ..........................
OR via Telephone ...........................
Time received: ………………...
Time received: ………………...
Email:
Email:
Fax:
Fax:
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
© Commonwealth of Australia 2011
Date: .....................
This page has been left blank intentionally.
52
© Commonwealth of Australia 2011
53
Writing a diagnostic report
When might you have to write a report on work you have done?

insurance repairs - where the insurer wants to know exactly what was done

disputes about repair work - a lawyer might want a written report about work done

careful owners - who want a written record of what was done to their vehicle

warranty work for another repairer or car dealer - eg when an interstate visitor breaks
down, and your workshop carries out repairs on behalf of a third party

research work - especially if you work in the development (experimental) area of a
vehicle manufacturer.
Why is it important to write a report in a standard way?
It helps to make sure that:

all the important parts of the work are covered

another person can understand what has been done

another technician can repeat your work if necessary (if it is part of a research or
development project).
The following section suggests the main headings that a report might contain.
© Commonwealth of Australia 2011
Parts of a Report
Contents

Useful for longer reports ( more than a few pages)

Helps a reader to quickly find what they want.
Introduction

Explains the reason for writing the report (why was the report requested? Who asked for
it?)

Summarises the symptom and task that the report covers.
Procedure

Explains exactly what was done during the diagnosis and repair. Don’t leave out anything
important

Identify any special test equipment used

A description of the conditions under which a test was done eg ambient temperature
and humidity for a performance test on a vehicle’s air conditioning system.
Results of tests and investigations

Record measured test results

A report on component condition (serviceability)

Might give details of specific test procedure/s, if that could affect the test outcome eg
measuring a/c pressures with or without a workshop fan in front of the condenser.
Conclusion

Explain what you have discovered/ observed/ concluded from your investigation of the
problem

What you believe caused the problem

What you have done to repair it

If you haven’t solved the problem, explain why.
Recommendations

54
Recommend any further action you believe is needed to make sure the problem stays
fixed (eg if you have just replaced an air filter element blocked with dust from unmade
country roads, you might advise that the service intervals for the vehicle should be
shortened from 10,000km to 5,000 km.)
© Commonwealth of Australia 2011
55
An example of a report
This report was written for the job described just a little earlier where the radio kept losing its
tuning pre-sets and the battery was replaced.
I’ve checked my records and the old battery
was still covered by warranty. Could you give
me a written report of the work done, so
that I can show the supplier of the old
battery that it was actually faulty? Then I can
claim against the warranty.
On the next page is the technician’s report. There is no contents page, because it’s quite short:
© Commonwealth of Australia 2011
Report on Job No. 1234 - Radio losing tuning pre-sets
Introduction
Report for Mr. A Person, owner of Daewoo Lanos, reg no. ABC 123, VIN KLATF08YE3B12345xxx.
Re: diagnosis and repair of the fault responsible for the following symptom: Radio loses tuning presets intermittently.
Procedure
Vehicle delivered with radio un-tuned (pre-sets had been lost). Owner said he could re-tune the radio
but the settings would be lost at irregular intervals, but only after an engine start.
Technician carried out the following checks:




Re-tuned radio without difficulty, and checked for normal operation- it performed correctly.
Visual inspection of radio and harness after re-tuning - no fault found.
Wriggle test in an attempt to re-create the problem- no fault found.
A series of engine re-starts. After the 11th re-start, the radio had lost its tuning pre-sets. Cranking
speed was slower than normal, so battery volt-drop suspected as the cause of the problem.
 A cranking voltage test indicated a battery problem, although a hydrometer test showed it to be
fully charged.
 Starter current draw was tested using a good slave battery, and alternator output was measured.
Both were found to be within specifications.
 A battery capacity test indicated a faulty battery. The battery was replaced with a newN480ZZ.
Results of tests and investigations
Operation of re-tuned radio
normal
Visual check
no faults found
Wriggle test
no faults found
Cranking voltage drop
10 volts- LOW
Starter current draw
80 amps- OK
Alternator output
14.4 volts @ 50 amps- OK
Battery specific gravity
12.65- OK
Battery capacity test
40%- faulty
Diagnosis
Inspection and testing of the systems connected with the radio showed that the radio circuit was
operational, but that a faulty battery suffered excessive voltage drop on starting, leading to radio
memory loss.
Repair
A new battery fixed the problem. Repetition of the start, re-start test confirmed the fault was
eliminated.
Recommendations
That this vehicle be regularly serviced, with special attention to regular checks of battery electrolyte,
terminal cleanliness, and mounting security to maximise battery service life.
56
© Commonwealth of Australia 2011
57
Activity 7
Write a report on a diagnosis and repair for a ‘third party’. This could be anyone outside of the
repair business - perhaps an insurance company or the manager of a vehicle fleet.
Base the report on the same repair you wrote the job card for in Activity 6 – “parking light not
working”. Use the information from that section to write your report.
The report form is on the next page.
Hints

Don’t bother with a contents page- your report won’t be that long!

Use the headings A to E provided.

Write in brief points – it’s not an essay! - but include all important details.
© Commonwealth of Australia 2011
STEADY EDDIE REPAIRS
Diagnostic Report on Job No. 5678
Introduction
Procedure
Results of tests and investigations
Conclusion
Recommendations
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
58
Date: .....................
© Commonwealth of Australia 2011
59
Other diagnostic approaches
Branching diagnostic procedures
The diagnostic procedures discussed previously are all linear – that is, each step must be completed
before you can do the next one. This approach works well for many vehicle faults, especially where
the technician only has to deal with one or two systems.
When a fault occurs in a more complex system, or in a system which has connections to other
systems, a branching diagnostic procedure might be used. This requires the technician to make
“yes / no” or “good / bad” decisions about various components or functions of a system.
It is sometimes called a “decision tree” or a “trouble tree”.
These procedures are sometimes provided by manufacturers in their workshop manuals.
If the procedure is followed correctly, the technician will eventually diagnose the faulty component
and be able to complete the repair.
Example: Part of a diagnostic procedure for checking a lubrication system
Oil level correct?
N
O
Pressure correct
at 250-280 kPa?
N
O
Clean/replace filter,
recheck pressure
Y
E
S
Pressure too
high
Pressure too
low
O
K
Y
E
S
N
O
T
Figure 6: Branching
diagnostic procedure
O
K
© Commonwealth of Australia 2011
Check for
restrictions
Y
E
S
N
O
Benefits of this procedure
The branched diagnostic procedure can speed up diagnosis.
As you gather your evidence, the procedure sets out the possible problems, and directs you to the
next question or test. Decision making is reduced to simple yes / no questions.
In modern vehicles, with multiple ECUs and bus communication systems, there is a high level of
interconnection between systems, and these procedures help you find your way logically through
the maze.
However, the technician’s skill and knowledge is still essential for testing or evaluation of
components.
CAUTION!
Be cautious when using a manufacturer’s branching diagnostic
procedure. There could be errors in the process so you shouldn’t just
follow it blindly.
As you work through the process, ask yourself if what you are doing is
logical and in the right order, and if the specifications quoted sound
sensible.
Also, they can’t take into account all the factors which are outside the
system, but which could still affect it. So you must keep these in mind
yourself.
60
© Commonwealth of Australia 2011
61
Activity 8
Branched Diagnostic Procedures
Design a simple “decision tree” (branched diagnostic procedure) for the symptom described below.
Make it simple and clear so that any other technician to follow your process.
Assume that the symptom has already been confirmed.
My car has been losing coolant.
I have to put in almost half a
litre every week!
Vehicle: 2004 base model 4 cylinder Korean import, manual transmission.
You could start with this step:
NO
Visually inspect cooling
system - evidence of
leaks?
© Commonwealth of Australia 2011
YES
Sketch your decision tree here.
Visually inspect cooling
system - evidence of leaks?
NO
YES
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
62
Date: .....................
© Commonwealth of Australia 2011
63
‘Black Box’ Diagnosis
Most vehicle systems now include an electronic control unit (ECU) as a master control unit. The ECU
is too complex to be repaired by the average workshop, but its functions can be fairly easily
understood. It is called a ‘black box’ because we know what the ECU does, but we don’t know (and
don’t need to know) how it does it.
Example:
Sensors
send
inputs to
ECU
E
C
U
ECU sends
outputs to
actuators
Figure 7: Diagram of a black box system
This diagram is a simple picture of a typical vehicle electrical or electronic system. The ECU is at the
centre, with a control job to do.

The ECU receives information (‘inputs’) from a variety of sensors which are connected to
the ECU by wires.

The ECU processes the inputs through its internal programming (which we don’t need to
know about).

Then it sends commands (‘outputs’) to external devices (‘actuators’) to carry out specific
actions. These actuators are also connected by wires to the ECU.
Sensors measure things like coolant temperature, manifold air temperature throttle position,
engine rpm, crank angle and road speed.
Actuators are used to control things like alter idle speed, ignition control, fuel injectors and EGR
control (Exhaust Gas Recirculation)
© Commonwealth of Australia 2011
What if the fault is in the black box?
Most vehicle ECUs are very reliable, but occasional failures can be caused by:

dry solder joints on circuit boards

water leaks, or

“zapping” by electrical spikes such as those caused by careless welding on the vehicle.
It is more likely that the sensors or actuators will develop faults. These faults can be found by the
normal diagnostic techniques described earlier. The ECU itself may be capable of testing whether
there are faults in the inputs or outputs.
If all of the sensors, actuators, connections, power supplies and earths connected to the ECU are
working, then the fault must be in the ECU itself.
CAUTION:
If all of your tests suggest that the ECU is faulty, re-check, then RE-CHECK again.
ECUs can be very expensive
64
© Commonwealth of Australia 2011
65
On-Board Diagnostics
All new cars sold in Australia from 2006 onwards must have On-Board Diagnostics (OBD). The
current system is version number two and is referred to as OBD 2. All manufacturers must
use the same basic system. Before this, many vehicles had some form of on-board
diagnostics, but each manufacturer had a different system.
What is OBD 2?
OBD 2 is designed to self-diagnose and report when a vehicle’s emission control system fails to
meet, or is likely to fail to meet, legal requirements for vehicle emissions.
OBD 2 is a universal system:

All manufacturers must use it

All manufacturers must use the same code numbers for the same emission-related faults

All cars must have the same data link connector

It must be easily accessible within about 600 mm of the driver’s seat - near the steering
column, or in the centre console.

All manufacturers must use the same communication protocol to allow access to the
DTCs

The emission-related codes must be accessible to any generic scan tool.
How does an OBD system help with diagnostics?
OBD systems are a valuable source of information. When a technician is gathering information early
in the diagnostic procedure, a vehicle with OBD can save a lot of time by providing some of that
information - how much, depends on how sophisticated the system is.
The first OBD systems often used a warning light on the instrument panel sometimes called a
‘Malfunction Indicator Light’ or a ‘Check Engine Light’.
© Commonwealth of Australia 2011
Malfunction Indicator light
Figure 8: Location of malfunction indicator light
This light could be made to blink or flash out a number code which could then be matched to the
manufacturer’s list of possible faults. The number code is called a Diagnostic Trouble Code.
Example:
VT Holden Data
Link Connector
Figure 9: Coded lights
66
© Commonwealth of Australia 2011
67
Example: Some of the Diagnostic Trouble Codes for a Holden VT 3.8 litre V6.
VT Holden V6 3.8 litre
12
13
14
15
16
17
18
19
21
22
23
24
25
26
No RPM signal
Right Hand (RH) No Oxygen Sensor Signal
Engine Coolant Temperature ECT - Signal Voltage Low
Engine Coolant Temperature ECT - Signal Voltage High
Engine Coolant Temperature ECT - Signal Voltage Unstable
PCM Error - ECT Circuit
EGR Flow Fault
Throttle Position (TP) Sensor Stuck
Throttle Position (TP) - Signal Voltage High
Throttle Position (TP) - Signal Voltage Low
Intake Air Temperature (IAT) - Signal Voltage High
No Vehicle Speed Sensor Signal - Auto Transmission
Intake Air Temperature (IAT) - Signal Voltage Low
Intake Air Temperature (IAT) - Signal Voltage Unstable
43
44
45
46
47
48
49
Knock Sensor Circuit Fault
Right Hand (RH) Lean Exhaust Indication
Right Hand (RH) Rich Exhaust Indication
No Reference Pulses While Cranking
18X Reference Signal Missing
Camshaft Position Signal Missing
Cam/Crank Signal Intermittent
63
64
65
76
78
Left Hand (LH) No Oxygen Sensor Signal
Left Hand (LH) Lean Exhaust Indication
Left Hand (LH) Rich Exhaust Indication
Short Term Fuel Trim (STFT) Delta High
Long Term Fuel Trim (LTFT) Delta High
96 AlC Pressure Sensor Fault
97 Canister Purge Circuit Fault
Some of these codes will turn on the ‘Check Engine’ light; others will not. See the workshop manual
for details.
To display the VT Holden codes:

switch OFF ignition and all accessories

bridge terminals 5 and 6 of the Data Link Connector located near the steering column
The ‘Check Powertrain’ light will then flash out any DTC codes, beginning with DTC 12 (because the
engine is not running).
© Commonwealth of Australia 2011
Reading codes and information with a scan tool
A scan tool or code reader is a device which plugs into the data link connector. It can:

access the vehicle’s ECU

display the DTCs on a small screen

clear codes from the ECU’s memory.
As manufacturers developed their own particular on-board diagnostics systems, they also
developed their own special scan tools to read their system. For example, a Holden dealer would
use Holden’s own Tech 2 scan tool to display and clear the codes listed above.
As OBD systems developed they became too complicated to continue using the flashing method of
code reading, and now the only way of accessing the codes is with a scan tool.
Figure 10: Reading codes with a scan tool
68
© Commonwealth of Australia 2011
69
Proprietary and generic scan tools
Manufacturer’s scan tools are known as ‘proprietary’ or ‘genuine’ scan tools. They are usually only
available within the dealer network. Independent automotive businesses cannot buy these tools.
Genuine scan tools
These can usually do more than just read DTCs. They may be able to:

allow the technician to see more information, such as the vehicle’s VIN

allow the technician to test the operation of output devices or actuators, such as cooling
fans, fuel pumps, window motors etc.

display a direct read-out of actual live data, such as current coolant temperature,
throttle position, or air conditioning pressure

upload new software to ECUs

carry out tasks such as programming replacement keys.
The trend amongst manufacturers now is to use a combined diagnostic and information system.
The vehicle is connected to a dedicated computer rather than to a hand-held scanner. The
computer is better able to deal with the highly sophisticated current OBD 2 systems. It may be able
to directly access a database which could include a digital workshop manual, diagnostic flow charts
and service bulletins. This information could speed up diagnosis.
Generic scan tools
These are generally less capable than the genuine types but are still extremely valuable for
extracting trouble codes and some live data. They are easily available from equipment suppliers.
Their capabilities can range from a basic code reader that simply displays a numeric code, to
scanners which almost match the genuine scan tool in usefulness. Most generic scan tools provide
adaptors (if needed) for the Data Link Connector, and either on-board software or cartridges to
allow the scanner to communicate with a wide range of vehicles.
© Commonwealth of Australia 2011
What information is available from an OBD system?
Early OBDs focussed on faults related to the powertrain (engine and transmission) and emission
controls. As they became more sophisticated, the amount and type of information expanded.
The modern OBD 2 systems can:

show live or current data (the actual values right now for various components, such as
air flow rate, current RPM, or ignition timing)

show ‘freeze frame’ data (the information captured by sensorsat the time the fault
occurred)

show stored Diagnostic Trouble Codes

show pending Diagnostic Trouble Codes (detected during current or last driving cycle)

clear Diagnostic Trouble Codes and stored values

test results, oxygen sensor monitoring (non Controller Area Network [CAN] only)

test results, other component/system monitoring (Test results, oxygen sensor
monitoring for Controller Area Network [CAN] only)

control operation of on-board components/ systems

request vehicle information.
Essential features of an OBD 2 system
Check Engine light
The system will verify a fault before turning on the light. A detected fault is stored as a pending
fault. If the same fault occurs on the next two driving cycles, the light will be turned on and the
fault is stored as a confirmed fault.
The light may be turned off again if that fault doesn’t happen again during the next three driving
cycles.
70
© Commonwealth of Australia 2011
71
Freeze Frame information
When a fault is first detected, the system must store at least the following information:

the fault code for the event that prompted the data to be stored

coolant temperature

engine speed

engine load

fuel pressure, if available

inlet manifold pressure, if available

fuel trim values, if available

open or closed loop operation

vehicle speed, if available.
Readiness testing
The system monitors and tests all emission-related components or systems during a specified drive
cycle. The ECU reports ‘Ready’ or ‘Not Ready’ for those systems when a scan tool is connected.
Some systems are monitored continuously, such as engine misfiring and evaporative emissions.
Other systems are monitored, but not continuously, such as the EGR, catalytic converter, air
conditioning etc.
During these tests the system may turn various sensors and actuators on or off to see what effect is
produced, and compare that effect with the expected result. Any variation outside of the
programmed limits will set a diagnostic trouble code.
Diagnostic Trouble Codes
a. Mandated codes
For any emission-related system, the codes are provided by the government and must be used no
matter what make the car is. The codes must be accessible by any OBD 2 scan tool.
The codes must have a letter followed by four numbers, like this: P0105. The meaning of the code is
the same for all manufacturers. In this case, P0105 means ‘Manifold Absolute Pressure/Barometric
Pressure Circuit Malfunction’, no matter what make of car it is.
b. Manufacturers’ codes
For any other system, like ABS, manufacturers can make up their own DTCs and they are not
obliged to give code access to non-proprietary scan tools (though many do).
© Commonwealth of Australia 2011
How OBD 2 codes work
There are probably thousands of possible OBD 2 codes. This is the way they are created.
P
0
1
15
Which vehicle system
triggered the code? 
Is the code mandated
or a manufacturer’s
own code?
What sub-system is
associated with the
fault?
Gives more detail of
the fault
P= Powertrain system
0 = Mandated code
(emissions)
1 = Fuel and air
metering
Many possibilities
1 = Enhanced OBD 2
code available for
use by any vehicle
maker
2 = Fuel and air
(injection circuit)
B= Body system
C= Chassis system
U= Unused, or
sometimes
communication faults
3 = Ignition or misfire
4 = Auxiliary emission
controls
5 = Vehicle speed and
idle control
6 = Transmission
P0115 is a powertrain
problem
P0115 is a mandated
code.
P0115 is a fault which
affects fuel and/or air
metering
15 indicates a fault in
the Coolant
Temperature circuit,
which would affect
fuelling
Vehicle System codes
P codes- Power train means engine and transmission sub-systems.
B codes- Body control systems like lighting, air conditioning, audio etc.
C codes- Chassis control systems like ABS, ESP, active suspension, traction control etc.
 Enhanced OBD 2 code - it is the manufacturer’s choice to make it available to a scan tool
72
© Commonwealth of Australia 2011
73
Body and Chassis Codes
Examples:
B0540 Speedo signal error (used by any / all manufacturers)
C0035 LHF wheel speed signal error (used by Holden)
Below is a sample list of OBD 2 ‘P’ codes:
These are just a few of the many codes possible.
P0010 A Camshaft Position Actuator Circuit (Bank 1)
P0011 A Camshaft Position - Timing Over - Advanced or System Performance (Bank 1)
P0012 A Camshaft Position - Timing Over - Retarded (Bank 1)
P0013 B Camshaft Position - Actuator Circuit (Bank 1)
P0014 B Camshaft Position - Timing Over - Advanced or System Performance (Bank 1)
P0015 B Camshaft Position - Timing Over - Retarded (Bank 1)
P0024 B Camshaft Position - Timing Over - Advanced or System Performance (Bank 2)
P0025 B Camshaft Position - Timing Over - Retarded (Bank 2)
P0026 Intake Valve Control Solenoid Circuit Range/Performance (Bank 1)
P0027 Exhaust Valve Control Solenoid Circuit Range/Performance (Bank 1)
P0028 Intake Valve Control Solenoid Circuit Range/Performance (Bank 2)
P0029 Exhaust Valve Control Solenoid Circuit Range/Performance (Bank 2)
P0068 MAP/MAF - Throttle Position Correlation
P0069 Manifold Absolute Pressure - Barometric Pressure Correlation
P0070 Ambient Air Temperature Sensor Circuit
P0071 Ambient Air Temperature Sensor Range/Performance
P0072 Ambient Air Temperature Sensor Circuit Low
P0073 Ambient Air Temperature Sensor Circuit High
P0074 Ambient Air Temperature Sensor Circuit Intermittent
P0095 Intake Air Temperature Sensor 2 Circuit
P0096 Intake Air Temperature Sensor 2 Circuit Range/Performance
P0097 Intake Air Temperature Sensor 2 Circuit Low
P0098 Intake Air Temperature Sensor 2 Circuit High
P0099 Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic
You can see that there is an enormous amount of information that could be available to a
technician trying to diagnose a fault.
How much information you can actually get depends on which codes the manufacturer has decided
to use, and whether the maker has given free access to any non- mandated, vehicle specific codes
as well.
© Commonwealth of Australia 2011
This page has been left blank intentionally.
74
© Commonwealth of Australia 2011
75
Activity 9
Tick the correct answer/s. There may be more than one.
Question 1
When using ‘black box’ diagnosis to find a fault, the technician must:

Replace any ECUs which are not coloured black

Test no more than three of the inputs to the ECU

Test all of the sensors, actuators, power supplies and earths connected to the black box

Open the black box and probe the circuit boards with a Phillips screwdriver.
Question 2
When discussing vehicle faults, the term ‘OBD’ means:

Out Board Depth

One Bad Device

On Board Diagnostics

Own Brand Diagnostics.
Question 3
What is OBD 2?

A compulsory on-board diagnostic system for all new cars since 2006

A voluntary on-board diagnostic system for all new cars since 2006

An on-board diagnostic system accessible by any OBD 2 scan tool

An on-board diagnostic system aimed at monitoring vehicle emissions.
© Commonwealth of Australia 2011
Question 4
The purpose of an OBD system is to:

Detect faults in vehicle systems and immobilize the vehicle until repairs are made

Detect faults in vehicle systems and alert the driver

Detect faults in vehicle systems and automatically fix the problem

Detect faults in vehicle systems and tell the technician where to look for faults.
Question 5
When a fault is detected in a vehicle system, the driver is alerted by:

An SMS message

E-mail

Malfunction indicator light

A voice message through the audio system.
Question 6
An OBD 2 system should be able to:

Show current data

Show ‘freeze frame’ data

Show stored Diagnostic Trouble Codes

Clear Diagnostic Trouble Codes and stored values

Show pending Diagnostic Trouble Codes.
Question 7
A ‘pending’ OBD 2 code is one which:
76

Does not turn on the ‘Check Engine’ light

Is set when a fault occurs once, but doesn’t appear again

Depends on the make of vehicle

Relates only to suspension systems.
© Commonwealth of Australia 2011
77
Question 8
‘Freeze frame’ data is:

The information captured by the ECU when a DTC occurred

Information that relates only to the climate control system

The data the system’s sensors were providing at the time a fault occurred

Information provided when the engine seizes.
Question 9
‘Live data’ is:

Only available if the technician is in the driver’s seat

The actual operating values for various parts of an operating system e.g. voltage

Provided only for components which have movement e.g. windscreen wipers

Available from any live electrical connection e.g. the positive battery terminal.
Question 10
What do these OBD 2 codes mean?

P0442

P0074

P0013

P0103

P0205
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
© Commonwealth of Australia 2011
Date: .....................
This page has been left blank intentionally.
78
© Commonwealth of Australia 2011
79
Activity 10
Ask your teacher to direct you to a vehicle or a system with a fault. Use any of the methods
described in this workbook, OR any other method available to you to diagnose the fault in the
vehicle or system.
You may use workshop manuals supplied by your teacher; textbooks; commercial information
sources; service bulletins; test equipment or scan tools to help you.
Remember to check the workshop manual for any suggested diagnostic approaches.
As you work through the diagnosis, record the steps you take and the results of any tests you
make. The record can be in the form of a step-by-step procedure, or it could be a ‘decision tree’.
Observe all relevant safety precautions while working.
Good luck!
Ask your trainer to check your results before proceeding.
Trainer Signature: ..............................................................
© Commonwealth of Australia 2011
Date: .....................
This page has been left blank intentionally.
80
© Commonwealth of Australia 2011
81
Glossary
WORD
MEANING
abnormal
Things are NOT okay, or NOT the way they should
be
abnormal event
When something happens NOT in the way it should
accurate
Correct, exact
actuators
Devices which carry out specific actions
confirm
Check that something is true
confirmed
Definite
data
Information
diagnosis
Finding the cause of a problem
efficient
Doing things well in the quickest time possible
eliminate
Get rid of
event
Something that happens
fault
Problem
faulty
Worn, broken, not working correctly
feedback loop
When you get some information from a check or
test, you use it to rethink what you will do next.
‘freeze frame’ data
Information which shows exactly what data the
system’s sensors were providing at the time the
fault occurred
hazard
Danger
inefficient
Taking longer than necessary to do something
input
Information going into a system
live data
Information from right now, such as current
coolant temperature, throttle position, or air
conditioning pressure
logical
Sensible
© Commonwealth of Australia 2011
WORD
MEANING
mandated
Required by law
minimum
Least
normal
Things are okay or the way they should be
normal event
When something happens in exactly the way it
should
output
Command or message going out
pending
Waiting
procedure
A logical set of steps to follow
productivity
Time spent per job
proprietary
Owned by the manufacturer
subsequent
Later
symptom
A clue that something is wrong.
systematic
Following a sensible order or system, not just any
way it happens
third party
First party - the car owner
Second party -the repair business
Third party – someone else eg an insurance
company, or the manager of a vehicle fleet
82
valid
True
ventilation
Fresh air
warranty
Manufacturer’s promise to replace a faulty item
© Commonwealth of Australia 2011