Instrument Panel Cluster (IPC) Description and Operation: Tachometer
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 engine speed based on Class 2 information from the powertrain control module (PCM) or the engine control module (ECM). The tachometer defaults to 0 rpm if a malfunction in communication exists.