Instrument Cluster Description and Operation: Speedometer

The engine control module (ECM) sends the vehicle speed to the instrument panel module (IPM) via GMLAN. The instrument panel cluster (IPC) displays the vehicle speed as determined by the IPM. The IPC receives a GMLAN message from the IPM indicating the vehicle speed. The speedometer will default to zero if:

• The ECM detects a malfunction in the vehicle speed sensor circuit.
• The IPC detects a loss of GMLAN communications with the IPM.
• The IPM detects a loss of GMLAN communications with the ECM.