Instrument Panel Cluster (IPC) Description and Operation: Tachometer

The IPC receives a discrete input from the ECM indicating vehicle speed. Each engine revolution is represents two input pulses to the ECM. The instantaneous engine speed is calculated by the ECM using the time difference between the two input pulses. The tachometer will default to 0 rpm if:

• The ignition is in OFF, ACCESSORY, or CRANK.
• The time duration since the last pulse is greater than or equal to one second.