Speedometer Head: Description and Operation

SPEEDOMETER

The instrument panel cluster (IPC) displays the vehicle speed based on the information from the body control module (BCM). The engine control module (ECM) calculates the vehicle speed based on the controlled area network (CAN) serial data message indicating the wheel reference speed from the electronic brake control module (EBCM). The ECM sends a CAN serial data message to the BCM indicating the vehicle speed. The BCM sends a class 2 message to the IPC indicating the vehicle speed.

The speedometer defaults to 0 km/h (0 mph) when any of the following occur:
- The EBCM detects a malfunction in the vehicle speed sensor circuit.
- The ECM detects a loss of CAN communications with the EBCM.
- The BCM detects a loss of CAN communications with the ECM.
- The IPC detects a loss of class 2 communications with the BCM.