Speedometer Head: Description and Operation

SPEEDOMETER

The instrument panel cluster (IPC) displays the vehicle speed based on GMLAN serial data message from the body control module (BCM). The BCM receives vehicle speed data from the powertrain control module (PCM)/engine control module (ECM) via the GMLAN serial data circuit. The speedometer will default to 0 km/h (0 mph) if:
- The PCM/ECM detects a malfunction in the vehicle speed sensor circuit.
- The BCM detects a loss of GMLAN communications with the PCM/ECM.
- The IPC detects a loss of GMLAN communications with the BCM.