Instrument Cluster Description and Operation: Speedometer

The instrument panel cluster (IPC) displays the vehicle speed as determined by the engine control module (ECM)/powertrain control module (PCM). The IPC receives vehicle speed information from the body control module (BCM) via a GMLAN serial data message. The speedometer defaults to 0 km/h (0 mph) when the IPC detects a loss of GMLAN communications with the ECM/PCM or the BCM.