Tachometer: Description and Operation

TACHOMETER

The IPC displays the engine speed on the analog tachometer based on the engine speed signal from the PCM. The IPC uses the engine speed signal circuit - 2 pulses/engine revolution - from the PCM in order to calculate the engine speed.

The IPC also receives a class 2 message from the PCM indicating the engine speed. The IPC compares the class 2 value to the engine speed signal from the PCM to determine if the engine speed is valid. When the IPC detects a malfunction in the engine speed signal circuit, the IPC uses the class 2 message from the PCM to indicate the engine speed.