3X Reference

The PCM uses this signal, from the ignition control module to calculate engine speed and crankshaft position over 1600 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 Crankshaft Position (CKP) High to Low Resolution Frequency Correlation will set and the PCM will use the 24X reference signal circuit for fuel and ignition control.

This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM.

The PCM compares voltage pulses on the reference input circuits to pulses on this circuit, ignoring pulses that appear on both.