Component Tests and General Diagnostics

When all tests and checks have been carried out in accordance with the diagnostics procedure for the relevant diagnostic trouble code, or by manual fault diagnosis, without any faults having been found, it is natural to assume that the control module is at fault. Therefore, go through all the following points very carefully before definitely pinpointing the Motronic control module as the cause of the fault.

1. Check once again that every single point in the diagnostic procedure for the diagnostic trouble code in question has been carried out.
2. Study the wiring diagram of the circuit in question and make sure you understand it. Relevant parts of the technical description and the electrical principles of operation described in the Electrical System, wiring diagrams may be of assistance in this respect.
The wiring diagram in this Motronic service manual was finalized about 10 weeks before the start of production. In the event of any differences as compared with the wiring in problem cars, the corresponding wiring diagram in the Electrical system, wiring diagrams is to be regarded as a reference.
3. In connection with removing/fitting the control module, bear in mind its sensitivity to electrostatic discharges. See "Handling Control Modules" for more information about this.
4. Check all grounding points and the control module's power supply. If you have already done so, do it once again. Check that power ground and sensor ground are physically and electrically separated from each other.
5. If the suggested fault diagnosis procedure does give the desired results, try to locate the fault by taking test readings and analysing them with the aid of "Test readings, Control Module Connections". Connect up a BOB or SIM.
6. According to statistics compiled for M93-M95, the majority of all Motronic control modules returned for repair under warranty are in perfect working order. Be restrictive with control module replacement.
Unnecessary control module replacement represents a sizeable cost item for Saab Automobile and Saab dealers. Give careful thought to all possible causes of the fault before changing the control module.
When substituting a control module for testing purposes, always refit the original unit.
7. If the original fault still persists in spite of this, then the Motronic control module will have to be changed.