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

The speedometer gives an indication to the vehicle operator of the vehicle road speed. This gauge is controlled by the IC circuit board based upon programming and electronic messages received from the BCM. The BCM is provided the vehicle speed information across the CAN data bus by either the ECM, the Electronic Stability Control (ESC) module or the Anti-lock Brake System (ABS) module.

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

• Vehicle Speed Message  - Each time the ECM receives an electronic vehicle speed  message from the ECM 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 about every 88 milliseconds. 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 ECM continually monitors the vehicle speed sensor to determine the vehicle road speed. The ECM then sends the proper vehicle speed messages to the IC. For further diagnosis of the speedometer or the IC circuitry that controls the gauge. Refer to DIAGNOSIS AND TESTING . The speedometer is serviced as a unit with the instrument cluster.