Initial Inspection and Diagnostic Overview

Fault Diagnosis Strategy For Electronic System

1 The customer's description of the problem is the basis for 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 technicians read out the diagnostic trouble codes from all systems.
A function fault in one system can often be caused by a fault in another system.
5 The car contains diagnostic trouble codes which are secondary faults or which are incorrectly set.
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, a fault search by symptoms can be carried out.
a In EPSI, carry out a fault search 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 the electronic system

Control module
When voltage is applied to the control module, the processor is turned on. The processor 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 program is incorrect, the diagnostic trouble code "Internal Control Module Fault" is given.
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 instrument.

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

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 diagnostic instrument.