efficient fault diagnosis 2

7/17/2019 Efficient Fault Diagnosis 2

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How To: Efficient Fault Diagnosis.

Interpreting Fault codes.

Diagnostics 2.TECHNICAL BULLETIN

To talk with a technical expert on this subject, call

00442078586890 or email [email protected]

With diagnostics becoming more and more essential to a garages survival, it is important that the

diagnostic procedure is as efficient as possible.

Many people use fault codes as the only diagnosis, and there is a lot to be learned from fault codes,

however more in depth diagnosis is often necessary.

This bulletin covers fault codes, but also shows a logical path to follow to resolve the concern.

It’s all very well getting detailed fault codes and data but this information is only useful if you

understand it. One problem associated with fault codes and the messages with those codes is trying

to interpret exactly what they mean.

A technician can learn a lot about a fault from the generated code that can be used to more

accurately pin point the fault and ultimately save the technician time in diagnosis and rectification of

the concern.

Fault codes are broken down into the following sections, each of which relates to a specific system

or sub-system.

P = Powertrain.

B = Body.

C = Chassis.

U = Communication.

For powertrain codes the following applies.

P0XXX and P2XXX are generic (NOT manufacturer specific) codes,P1XXX and P3XXX are manufacturer specific codes.

For body, chassis and communication codes the following applies.

B0XXX and B3XXX are generic (NOT manufacturer specific) codes.

B1XXX and B2XXX are manufacturer specific codes.








The third digit indicates a sub menu, (detailed below).

1 = Fuel and Air.

2 = Fuel and Air Metering.

3 = Ignition System or Misfire.

4 = Auxiliary Emission Control System.

5 = Vehicle Speed Control and Idle Control System.

6 = Computer Output Circuits.

7 = Transmission.

8 = Transmission.

From the above information we can see that a code of P0301 for example reads as a generic

powertrain code showing an ignition system fault or misfire on cylinder number one. Although this

information is useful further checks are necessary to determine the exact cause of the fault.

It is also worth remembering that just because a warning lamp is not illuminated, that does not mean

that a fault is not present. It is possible that the fault has happened for long enough to be logged by

the ECU, or that the code is not recognised by the diagnostic tester.

It is therefore important to make use of all the equipment at your disposal, such as live data, exhaust

gas analysers, fuel pressure testers and oscilloscopes, to make your job as straight forward aspossible.

The following flow chart shows a logical approach to the use of fault codes and the additional

diagnostics that may be required to efficiently diagnose faults.








Connect Diagnostic

Equipment.

Identify Fault Code.

Exact fault

located.Carry out Repair.

Fault

code

cleared.

Carry out Roadtest.Concern

Rectified.

Return Vehicle to

Customer.

Carry out Pinpoint

Diagnostics.

Yes

Yes

NoYes

No

No

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