Gauge Pack, Instrument Cluster: Operation: Speedometer

The speedometer gives an indication to the vehicle operator of the vehicle road 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 vehicle speed information across the Controller Area Network (CAN) data bus by the Antilock Brake System (ABS) module (also known as the Brake System Module/BSM).

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

• Vehicle Speed Message  - Each time the IC receives an electronic vehicle speed  message from the BCM it will calculate the correct vehicle 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 positioned at the relative vehicle speed position on the gauge scale until the vehicle stops moving, 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 ABS module continually monitors the wheel speed sensors to calculate the vehicle road speed and distance. The ABS module then sends the proper vehicle speed messages to the BCM over the CAN data bus, and the BCM relays those messages to the IC. For proper diagnosis of the wheel speed sensors, the ABS module, the BCM, the IC, the CAN data bus or the electronic communication related to speedometer operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.