Advanced Automotive Fault Diagnosis

(New book out in a few months…)

Six-stages of fault diagnosis

When a customer reports a fault here is a process to follow:

1. Verify: Is there actually a problem, confirm the symptoms

2. Collect: Get further information about the problem

3. Evaluate: Stop and think about the evidence

4. Test: Carry out further tests in a logical sequence

5. Rectify: Fix the problem

6. Check: Make sure all systems now work correctly


Here is a very simple example to illustrate the diagnostic process. The reported fault is excessive use of engine oil.

1. Question the customer to find out how much oil is being used (is it excessive?).

2. Examine the vehicle for oil leaks and blue smoke from the exhaust. Are there any service bulletins?

3. If leaks are found the engine could still be burning oil but leaks would be a likely cause.

4. A compression test, if the results were acceptable, would indicate a leak to be the most likely fault. Clean down the engine and run for a while. The leak will show up better.

5. Change a gasket or seal, etc.

6. Run through an inspection of the vehicle systems particularly associated with the engine. Double check the fault has been rectified and that you have not caused any further problems.

Be logical, that’s the secret!

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