Instrument Panel Cluster (IPC) Description and Operation: Tachometer
WARNING: This page is about a different car, the 2002 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
The IPC displays the engine speed based on information from the PCM. The PCM converts the data from the engine speed sensor to a 2 pulses/engine revolution signal. 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 (2 pulses/engine revolution) exists.