18X Reference PCM Input

The ICM sends the 18X reference signal to the PCM. The PCM uses this signal to calculate engine RPM and CKP at engine speeds below 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 P0336 is set and the PCM uses the 3X reference signal circuit at all times for fuel and ignition control. The engine continues to start and run using the 3X reference signal only. Refer to Electronic Ignition System Description for further information.