3X Reference PCM Input

The ignition control module (ICM) sends the 3X reference signal to the powertrain control module (PCM). The PCM uses this signal to calculate the engine RPM and crankshaft position (CKP) at engine speeds above 1200 RPM. The PCM also uses the pulses on this circuit to initiate injector pulses. If the PCM receives no pulses on this circuit, DTC P1374 is set and the PCM uses the 18X reference signal circuit for fuel and ignition control. The engine continues to start and run using the 18X reference signal only. Refer to Electronic Ignition System Description for further information.