Instrument Panel Cluster (IPC) Description & Operation: Tachometer
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The IPC displays the engine speed based on the engine speed signal from the PCM. The IPC uses the engine speed signal circuit (2 pulses/engine revolution) from the PCM in order to calculate the engine speed. The tachometer defaults to 0 RPM if a malfunction in the engine speed signal circuit exists.