3. Knowing the likelihood of occurrence of faults

fact, may be an important clue for locating the cause.

3. Knowing the likelihood of occurrence of faults

Knowing the likelihood of occurrence of faults

It is wise not to forget simple things which are often solved more easily than complicated ones (e.g. electric faults occur more frequently due to simple slackened connections rather than the actual failure of a component).

Also remember that all the parts of the car, even if they are new, may be subject to faults: this is highly improbable, but not impossible. Of course, the “older” and worn the parts, the more this probability rises.

4. Do not cure the symptom without eliminating the cause

Certain operations remedy a defect temporarily but do not remove the cause that originated the defect.

Examples:

• merely replacing a fuse without investigating the possible cause that triggered the overcurrent;
• topping up a level, without locating the leak of a certain fluid in the circuit.

PHASES OF THE DIAGNOSIS PROCEDURE

Below we are giving a detailed examination of the diagnosis process as it is taught in the training courses for Dealer Expert technicians.

The basic phases of the process are:

• Phase 1 - Analysis of the situation
• Phase 2 - Diagnosis procedure
• Phase 3 - Testing and approval

Phase 1:
Analysis of the situation

This phase is characterised by three moments with a result that has a determinant effect on the process:

• 1.1 Interview with the customer
• 1.2 Road test
• 1.3 Consulting the technical literature.

1.1. Interview with the customer

– On the basis of the symptoms reported by the customer (e.g. “The car will not start”). The receiver should reformulate the description of the fault to frame the symptom in correct terminology.

To do this, he should go into further details of the description of the symptom through suitable questions, such as for example:

• What happens? (the starter motor turns but the engine does not start etc.)
• when does the symptom occur? (always, at each attempt to start, etc.)
• where? (everywhere: in town, on the motor-way, etc.)
• how does it occur (with all three keys).

At the end of the interview the receiver will be able to re-formulate the fault:

The car does not start
even after a number of attempts
and with the use of all the keys available.
The code warning light stays on

1.2. Road test

This is proposed when the receiver needs to verify for himself the conditions in which the fault occurs.

1.3. Consulting technical literature

This mainly consists in consulting the following documents:

• Service manual
• Service News
• Recovery campaigns

In many cases only consulting the technical literature will be sufficient to direct the technician to the real cause of the fault.

Phase 2:
Diagnosis procedure

A. Selection of the possible causes

With the fault reported and re-formulated by the receiver, the technician should:

• Take into consideration all the possible causes that could be represented graphically with the following cause-effect diagram.
• analyse each cause to make choices.

Initially it might be helpful to proceed by exclusion:

• Which causes do not explain the facts?
  – uncertain earth
  – supply failure
  – key not recognised