Instrument Panel Cluster (IPC) Description and Operation: Speedometer
WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
The instrument panel cluster (IPC) displays the vehicle speed based on Class 2 information from the powertrain control module (PCM) or the engine control module (ECM) or the Anti-lock Brake System (ABS) module. If the vehicle is equipped with ABS the speedometer defaults to 0 mph (0 km/h) or last known state if a malfunction in communication exists.