3X Reference PCM Input

The Powertrain Control Module (PCM) uses this signal from the Ignition Control Module (ICM) to calculate the engine RPM and the Crankshaft Position (CKP) at engine speeds of more than 1200 RPM. The PCM also uses the pulses on this circuit to initiate the fuel injector pulses. If the PCM does not receive pulses on this circuit, DTC P1374 sets and the PCM uses the 18X reference signal circuit for fuel control and for ignition control. The engine continues to start and run using the 18X reference signal.