Gauge Pack, Instrument Cluster: Operation: Operation: Tachometer

The tachometer gives an indication to the vehicle operator of the engine speed. This analog gauge is controlled by the Instrument Cluster (IC) (also known as the Instrument Panel Cluster/IPC) electronic circuit board based upon programming and electronic messages received from the Body Control Module (BCM). The BCM is provided the engine speed information across the Controller Area Network (CAN) data bus by the Powertrain Control Module (PCM) (also known as the Engine Control Module/ECM).

The IC controls the gauge needle position and provides the following features:

• Engine Speed Message  - Each time the IC receives an electronic engine speed  message from the BCM 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 message and reposition the gauge pointer accordingly numerous times in every passing second. 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 a 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 BCM over the CAN data bus, and the BCM relays those messages to the IC. For proper diagnosis of the crankshaft position sensor, the PCM, the BCM, the IC, the CAN data bus or the electronic communication related to tachometer operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.