Tachometer: Testing and Inspection

Fault symptoms
Tachometer inoperative

Diagnostic procedure
1 Check the power supply.
Does the fuel gauge work?
YES Continue with point 2
NO Rectify the power supply
2 Check the rpm signal
- Unplug main instrument display panel connector 12p-1. Connect the Intellegent Saab Tester (ISAT) scan tool test leads to pin 4 and a good ground.
- Select 'TEST" and then "PULSE".
- Start the engine.
The ISAT scan tool should show about 30 Hz at idling speed. Is this reading obtained?
YES Change the main instrument display panel and continue with point 3.
NO Check the lead between pin 6 of the Motronic control module and pin 4 of the main instrument display panel's 12p-1 connector. Rectify as necessary and then continue with point 3.
3 Final check
Functionality OK?
YES The steps taken to rectify the fault were correct.
NO Continue fault diagnosis as described in "Powertrain Managment".