P1374

Circuit Description
The 3X reference signal is produced by the Ignition Control (IC) Module. The IC Module calculates the 3X reference signal by dividing the Crankshaft Position (CKP) sensor 7X pulses by 2 when the engine is running and the CKP synchronizing pulses are being received. The PCM uses the 3X reference signal to calculate the engine RPM and the Crankshaft Position at engine speeds above 1600f150 RPM. The PCM also uses these pulses to initiate injector pulses. The PCM compares the 3X reference pulses to the 24X CKP pulses and the CMP pulses. If the PCM receives an incorrect number of pulses on the 3X circuit a DTC P1374 will set and the PCM will use the 24X CKP reference circuit for fuel and Ignition Control. The engine will continue to start and run using only the 24X CKP and Camshaft Position Sensor signals.

Conditions for Running the DTC
The engine is running (24X reference pulses are being received).

Conditions for Setting the DTC
^ The ratio of 24X reference pulses to 3X reference pulses received by the PCM does not equal 8.
^ The ratio of 24X reference pulses to camshaft position PCM input pulses received by the PCM equals 48.
^ The conditions are present for greater than 10 seconds.

Action Taken When the DTC Sets
^ The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.
^ The MAP Sensor reading will freeze when the 3X signal is lost. (Refer to Diagnostic Aids for further operation.)

Conditions for Clearing the MIL/DTC
^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool.

Diagnostic Aids
DTC P1374 can be caused by secondary components leaking high voltage into the IC Module. Check for the following conditions:
^ Incorrect harness routing near secondary ignition components.
^ Ignition coil arcing to wiring harness or IC Module (check ignition coils for cracks, carbon tracking, or other signs of damage).
^ Secondary ignition wire(s) arcing to wiring harness.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:
^ Poor connection. Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Intermittents and Poor Connections Diagnosis. Refer to Repairing Connector Terminals in Diagrams.
^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition on and observe a voltmeter connected to the 3X reference circuit at the PCM harness connector while moving connectors and wiring harnesses related to the IC Module. A change in voltage will indicate the location of the fault. Refer to Wiring Repairs.
^ The MAP Sensor reading will freeze when the 3X signal is lost.
1. After the MAP sensor freezes, DTC P0101 Mass Air Flow (MAF) Sensor Performance may set due to the incorrect MAP Value and the engine may be hard to start (possible long crank).
2. Eventually (after a long crank) a DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage may also set and replace the MAP Sensor value with a default value and the engine will start and regain some performance. Symptom Related Diagnostic Procedures

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description
The numbers below refer to the step numbers on the diagnostic table:
10. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.