Instrument Panel Cluster (IPC) Description and Operation: Tachometer
WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
The instrument panel cluster (IPC) displays the engine speed as determined by the powertrain control module (PCM). The IPC receives a class 2 message from the PCM indicating the engine speed.