Fault Diagnosis, Strategy For Electronic Systems

Fault Diagnosis Strategy For Electronic Systems

1 The customer's description of the trouble forms the basis of the fault diagnosis strategy.
If necessary, the customer must demonstrate the problem on the car to avoid misunderstandings.
2 In certain cases, the function may be correct.
a Good product knowledge is required to decide this.
b If the function is correct, this must be explained to the customer.
3 If the function is considered faulty, the car should be repaired.
Saab's fault diagnosis strategy assumes that the technicians are familiar with the customer's description of the problem. So note the customer's complaint and any other comments on the job sheet.
4 The technician obtains readouts 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 erroneously generated.
a Compare the customer's complaint with the symptom descriptions for the various diagnostic trouble codes. EPSI has a fast search path for this.
b If the symptom descriptions for a diagnostic trouble code match the customer's complaint, this is probably the cause of the primary fault.
Repair as instructed.
6 If there is no match with the diagnostic trouble codes, fault diagnosis by symptoms can be carried out.
a Look in EPSI under fault diagnosis by symptoms in the system where the fault has occurred.
b If the symptom descriptions in the current system match the complaint, the right fault diagnosis description has probably been found.
Repair as instructed.
7 If there is no match with the diagnostic trouble codes or symptoms, the technician must diagnose the fault himself.
A final check must be carried out after the repair. Good technical product knowledge is required to solve this type of problem.
8 The car is ready.

General Fault Diagnosis In Electronic Systems

Control module
When the control module is supplied with current, the processor is awakened. The processor then reads the instructions stored in the control module's memory.

The control module is programmed to read the inputs and activate the outputs. If the control module's program is faulty, the diagnostic trouble code "Internal Control Module Fault" is generated. If this fault code is not generated, the control module is almost always working as it should.

The control module must be switched on before the system will function. The control module is on and the processor alerted when the control module can be contacted by the diagnostic tool.

Outputs
The purpose of the system is to control a number of functions via various actuators, e.g. an injector or bulb. For the system to be able to perform its functions, it must be possible to activate the actuators. The actuators must therefore be connected to the control module and have the correct power supply or ground.

The functions of the control modules can be tested using the activation command on the diagnostic tool.

Inputs
Before the control module can control its actuators, the system sensors must supply the correct value to the control module.

The function of the sensors can be tested using the read command of the diagnostic tool.