Circuit Description

The 24X reference signal is used to improve idle spark control at low engine speeds. PCM uses the 24X reference signal to calculate engine RPM and crankshaft position at engine speeds less than 1600 RPM. PCM constantly monitors the number of pulses on the 24X reference circuit and compares the number of 24X reference pulses to the number of 3X reference pulses and CAM signal pulses being received. If PCM receives an incorrect number of pulses on the 24X reference circuit, DTC will set and PCM will use the 3X reference signal circuit for fuel and ignition control. Engine will continue to start and run using the 3X reference and CAM signals only. DTC will set when PCM receives incorrect number of pulses. For duplication of DTC, ensure engine is running and PCM is receiving 3X reference pulses for a minimum of 3 seconds.