The 3X reference signal is produced by the ignition control module (ICM). The ICM calculates the 3X reference signal by dividing the crankshaft position (CKP) sensor 18X pulses by 3. This calculation is performed while the engine is running, and while the CKP sync pulses are being received. The powertrain control module (PCM) uses the following information:
The 3X reference signal in order to calculate the engine RPM, and the CKP at engine speeds above 1,200 RPM
The pulses on the circuit in order to initiate injector pulses
A constant monitoring of the number of pulses on the 3X reference circuit
A comparison to the number of 3X reference pulses to the number of 18 X reference pulses and CAM signal pulses being received
If the PCM receives an incorrect number of pulses on the 3X reference circuit, DTC P1374 will set and the PCM will use the 18X reference signal circuit for fuel and ignition control. The engine will continue to start and run using the 18X reference and camshaft position (CMP) PCM input signals only.
This would have to be checked by GM or competent garage as P1xxx codes are manufacturer specific.
P0xxx codes are generic OBDII codes applicable to all OBDII PCM's.
Tuesday, March 30th, 2010 AT 9:10 AM