Instrument Panel Cluster (IPC) Description and Operation: Tachometer
WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. 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)/engine control module (ECM). The tachometer defaults to 0 RPM if the IPC detects a loss of class 2 communication with the PCM/ECM.