Tachometer Out Of Order

OUTPUT SIGNAL TO MAIN INSTRUMENT DISPLAY PANEL





Fault Symptoms.
Tachometer out of order. If a TCS diagnostic trouble code is present, proceed according to the diagnostic procedure for the code in question.

Diagnostic Help.
The tachometer can be activated with the ISAT scan tool.
- Select "ACTIVATE".
- Select "ENGINE RPM".

The command activates the tachometer, which should indicate 1000 rpm for 30 seconds.

The command activates the Motronic control module, causing it to send a 50 Hz signal to the tachometer. The tachometer should then indicate about 1000 rpm.

Check The Wiring.
Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.





Diagnostic Procedure.
1. Check the control module's output
- Unplug the main instrument display panel connector.
- Take a voltage/frequency reading across pin 2 and battery negative (B-).
- Connect the ISAT Scan Tool.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "ENGINE RPM".
The command activates output voltage, which should be about 5.5-6 V and 50 Hz.

Is the reading obtained OK?

YES: Continue fault diagnosis in the Electrical system, main instrument display panel.
NO: Continue with point 2.

2. Check The Wiring
- Check the continuity of the wiring between pin 80 of the Motronic control module and pin 2 of the main instrument display panel.

Is the wiring OK?

YES: Continue as described at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: Repair or replace the wiring.