Circuit Description

PCM supplies ground to energize the tachometer. When ignition switch is first turned on, the PCM grounds the tachometer circuit. Circuit will remain grounded until PCM receives the first 18X reference pulse. Once the 18X reference pulse is received, PCM controls the pulse in relationship to engine RPM. Tachometer is controlled at a rate of 2 pulses per crankshaft revolution. DTC will set when PCM detects an incorrect voltage on tachometer control circuit.