Speedometer Head: Description and Operation

Speedometer/Odometer


The PCM calculates the vehicle speed from the transmission output shaft speed (OSS) sensor input and from the tire size and axle ratio configuration in the PCM vehicle identification (VID) Block. On diesel engines, the PCM receives the OSS data from the transmission control module (TCM). The PCM provides the instrument cluster with the vehicle speed data over the HS-CAN bus. The instrument cluster monitors the vehicle speed input and commands the speedometer with a corresponding movement of the pointer.

The SELECT/RESET button has three functions. First, pressing the SELECT/RESET button will toggle between the odometer and trip odometer settings. When the trip odometer is displayed, pressing and holding the SELECT/RESET button will reset the trip odometer. There are two trip odometers available: A and B. Pressing the SELECT/RESET button while in trip odometer will toggle between trip odometer A and trip odometer B. Lastly, the instrument cluster self-test is entered by pressing and holding the SELECT/RESET button down with the key in the OFF position, then turning the key to RUN.

The instrument cluster receives odometer rolling count status from the PCM and stores the mileage in non-volatile memory (NVM). When the instrument cluster fails to receive the odometer rolling count status for more than 5 seconds, the odometer display will show dashes.