Instrument Cluster Description and Operation: Tachometer

The IPC receives a discrete input from the ECM indicating the engine speed. The engine speed signal circuit is pulled up to controlled B+ 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 ECM detects a malfunction in the engine speed signal circuit.