Tachometer: Description and Operation

The IPC displays the engine speed as determined by the BCM via a class 2 message. The BCM receives a class 2 message from the PCM indicating the engine speed. The tachometer will default to 0 rpm if:
^ The PCM detects a malfunction in the engine speed sensor circuit.
^ The IPC detects a loss of class 2 communications with the BCM.
^ The BCM detects a loss of class 2 communications with the PCM.