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Fault diagnosis, tachometer (rev counter) (MIU 2)

Fault diagnosis, tachometer (rev counter) (MIU 2)

Fault symptom

Tachometer needle does not move.

Diagnostic procedure



1. Start the engine.

2. Connect the ISAT Scan Tool and select "READ VALUES" followed by "ENGINE RPM".

3. Increase and decrease engine speed. If the rpm signal is OK, a corresponding increase and decrease (in rpm) should be shown on the Scan Tool's display.

If this is the case, continue with point 7.

4. If no rpm signal is present, check the signal sent to the main instrument display panel by connecting a BOB to the 56-pin connector behind the main instrument display panel (which should not be connected).



Connect the ISAT Scan Tool's test leads to pin 6 and ground. Then select "TEST" followed by "PULSE". Start the engine and check whether any pulses are generated. About 40 Hz (4 cyl.) at idling speed. About 30 Hz (6 cyl.) at idling speed.

If pulses are generated, proceed to point 8.

5. If no pulses are generated, check the wiring by connecting another BOB to the connector of the engine management system's control module.


The control module should not be connected.

6. Check for continuity/shorting to ground by taking a reading across pin 6 on

The BOB connected to the main instrument display panel and the engine management system.

If the wiring is OK, continue with engine management system fault diagnosis as described in Service Manual 2:7.

7. Select "TEST FUNCTIONS" followed by "TACHOMETER TEST" on the ISAT Scan Tool.


If in proper working order, the rev counter needle should rise to 7000 rpm and then return to 0.

If the tachometer does not work, it could be due to an open circuit in the connection between the processor card and the intermediate part of the main instrument display panel.

Remove the back of the main instrument unit complete with processor card and check that all leads to the connector marked CN3 are located securely. If any lead has come loose or is broken, continue on .

If the leads to the connector are all OK, the fault is probably in the intermediate part with the indicating instruments. Continue on .

8. Select "TEST FUNCTIONS" followed by "TACHOMETER TEST" on the ISAT Scan Tool. If in proper working order, the rev counter needle should rise to 7000 rpm and then return to 0.

If the tachometer works, there is probably an open circuit between the connector and the processor on the processor card in the main instrument unit. Continue on .