System Operation: Speedometer

The speedometer is an analog gauge. The BCM receives the vehicle speed message from the ABS module. The ABS module uses tire size stored in the vehicle configuration file along with wheel speed inputs to generate a vehicle speed signal. The BCM provides the vehicle speed message to the IPC.

If the vehicle speed message is missing or invalid for 1 second or less, the IPC defaults the speedometer to the last speed indication based upon the last known good message received.

The IPC provides a tolerance that allows the speed indication to display between 3% below and 7% above the actual vehicle speed. This means that with an actual vehicle speed of 96.6 km/h (60 mph), the speedometer can indicate between 93.7-103.3 km/h (58.2-64.2 mph). Incorrect tire size or tire size configuration could potentially affect the speedometer accuracy.