Instrument Cluster Description and Operation: Tachometer

The instrument panel cluster (IPC) receives a discrete input from the engine control module (ECM) indicating the engine speed. The engine speed signal circuit is pulled up to controlled battery voltage in the IPC. Each engine revolution represents 2 input pulses to the ECM. The instantaneous engine speed is calculated by the ECM using the time difference between the 2 input pulses. The tachometer will default to 0 RPM if the ignition is in OFF, ACCESSORY, or CRANK