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 trouble 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 judged to be faulty, the car should be repaired.
Saab's fault diagnosis strategy assumes that the mechanic is familiar with the customer's description of the trouble. So note the customer's complaint and any other observations on the job sheet.
4 The mechanic obtains readouts of 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 have diagnostic trouble codes which are secondary faults or which have been 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 diagnostic trouble code is probably caused by the primary fault.
Repair in accordance with the instructions.
6 If there is no match with the diagnostic trouble codes, fault diagnosis by symptoms can be carried out.
a In EPSI, look under fault diagnosis by symptoms in the system where the fault has occurred.
b If the symptom descriptions in the relevant system match the complaint, the right fault diagnosis description has probably been found.
Repair in accordance with the instructions.
7 If there is no match with the diagnostic trouble codes or symptoms, the mechanic will have to diagnose the fault using his own judgement and experience.
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, its processor will be awakened. The processor then reads the instructions stored in the control module 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" will be generated.
The control module must be supplied with current for the system to be operative. The control module is supplied with current and the processor awake when the control module can be contacted by the diagnostic instrument.

Outputs
The purpose of the system is to control a number of functions by means of different actuators, e.g. an injector or light bulb. For the system to be capable of performing 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 connection.

Inputs
Before the control module can control its actuators, the system sensors must supply it with the correct values.
The functionality of the sensors can be checked with the diagnostic instrument.