Gauge Pack, Instrument Cluster: Operation: Operation: Gauges: Tachometer

The tachometer gives an indication to the vehicle operator of the engine speed. This gauge is controlled by the IC circuit board based upon programming and electronic messages received from the PCM over the CAN data bus.

The tachometer is a stepper motor design gauge that receives battery current on the IC electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The IC is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The IC circuitry controls the gauge needle position and provides the following features:

• Engine Speed Message  - Each time the IC receives an engine speed message from the PCM it will calculate the correct engine speed reading and position the gauge needle at that relative speed position on the gauge scale. The IC will receive a new engine speed message and reposition the gauge pointer accordingly about every 88 milliseconds. The gauge needle will continually be repositioned at the relative engine speed position on the gauge scale until the engine stops running, or until the ignition switch is turned to the OFF position, whichever occurs first.
• Communication Error  - If the IC fails to receive an engine speed message, it will hold the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After three seconds, the gauge needle will return to the left end of the gauge scale.

The PCM continually monitors the crankshaft position sensor to determine the engine speed. The PCM then sends the proper engine speed messages to the IC. For further diagnosis of the tachometer or the IC circuitry that controls the gauge. Refer to DIAGNOSIS AND TESTING . The tachometer is serviced as a unit with the instrument cluster.

The gauges are diagnosed using the IC self-diagnostic test. Refer to DIAGNOSIS AND TESTING . Proper testing of the CAN data bus and the electronic data bus message inputs to the IC that control each gauge require the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.