Flow of Diagnosis

Fault Diagnosis Strategy For Electronic Systems






1. The customer's description of the problem constitutes a basis for the fault diagnosis strategy.

If necessary, the customer must demonstrate the trouble on the car to avoid misunderstandings.

2. In certain cases, the function may be correct.
2.a. Good product knowledge is required to decide this.
2.b. If the function is correct, this must be explained to the customer.

3. If the function is judged to be faulty, the car should be repaired.
Saab's fault diagnosis strategy assumes that the technician is familiar with the customer's description of the problem. So note the customer's complaint and any other observations on the job sheet.

4. The technician obtains a readout of the diagnostic trouble codes from all systems.
A malfunction in one system can often be caused by a fault in another system.

5. The car may contain diagnostic trouble codes which are secondary faults or which have been incorrectly generated.
5.a. Compare the customer complaint with the symptom description for the various diagnostic trouble codes. WIS has a quick search function for this purpose.
5.b. If the symptom description for a diagnostic trouble code matches the customer's complaint, this diagnostic trouble code is probably caused by the primary fault.

Repair as per instructions.

6. If there is no match with diagnostic trouble codes or symptoms, the technician must diagnose the fault himself.
6.a. Search in WIS under fault diagnosis for symptoms in the system where the fault exists. Also check whether there is a TSB/MI in force.
6.b. If the symptom description in the current system matches the complaint, the right fault diagnosis description has probably been found.

Repair as per instructions.

7. Certain fault symptoms can be remedied by reprogramming the control module.
7.a. Does the customer complaint stem from a known software problem in a programmable control module?
7.b. Reprogram the control module following the instructions in SPS.

8. If there is no match with diagnostic trouble codes or symptoms, the technician must diagnose the fault himself.

Good technical product knowledge is required to solve this type of problem.

9. A final check must be carried out after the repair.
10. The car is ready.