No Check Engine Lamp During Transmission Fault

Fault Symptom
The CHECK ENGINE lamp (MIL) does not light up inspite of a transmission fault that activates the limphome mode (emergency operation program).

Conditions
A fault in the ongoing drive cycle generates a diagnostic trouble code and causes the CHECK ENGINE lamp (MIL) to light up.

Diagnostic Help
The CHECK ENGINE lamp (MIL) can be activated from the transmission control module using an ISAT scan tool.
Select "AUT TRANSMISSION".
Select "ACTIVATE".
Select "CHECK ENGINE".





Procedure
1. Check the transmission control module output

- Plug a BOB into the engine control module's connector but do not connect the control module.
- Connect a test lamp to pins 61 and 60 (Saab Trionic), pins 65 and 58 (M4.1) or pins 39 and 54 (M5.2).
- Turn the ignition switch to the ON position.
The test lamp should then light up for about 1 second and then go out. If an on-board diagnostic 11 diagnostic trouble code is stored in the memory, the test lamp will start flashing. If there is no on-board diagnostic 11 diagnostic trouble code stored, the lamp will remain out.

Does the lamp work OK?

YES: Continue fault diagnosis in the Engine management system. Then proceed to point 3.
NO: Continue with point 2.





2. Check The Wiring between the transmission control module and the engine control module

Check the continuity of the wiring between pin 5 of the transmission control module and pin 61 (Saab Trionic), pin 65 (M4.1) or pin 39 (M5.2) of the engine control module.

Is the wiring OK?

YES: Continue with point 3.
NO: Rectify the fault and continue with point 3.





3. Final check
- Connect the ISAT scan tool.
- Select "ACTIVATE".
- Select "CHECK ENGINE".
The lamp should start flashing.

Is the lamp flashing?

YES: The remedial action taken was correct.
NO: Continue as described under "Before Changing A Control Module". Before Changing A Control Module