The 3X reference signal is produced by the ignition control module. The ICM calculates the 3X reference signal by dividing the Crankshaft Position (CKP) sensor 18X pulses by 3 when the engine is running and CKP sync pulses are also being received. The PCM uses the 3X reference signal to calculate engine rpm and crankshaft position at engine speeds above 1200 rpm. The PCM also uses the pulses on this circuit to initiate injector pulses. The PCM constantly monitors the number of pulses on the 3X reference circuit and compares 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 PCM input signals only.
Conditions for Setting the DTC
• The engine is running (18X reference pulses are being received).
• The ratio of 18X reference pulses to 3X reference pulses received by the PCM does not equal 6:1.
• The ratio of 18X reference pulses to CAM signal pulses received by the PCM equals 36:1.
• Above conditions are present for 80 occurrences.
Action Taken When the DTC Sets
• The PCM will illuminate the MIL during the second consecutive trip in which the DTC test has run and failed.
• The PCM will use the 18X reference signal circuit for fuel and ignition control.
• If equipped with traction control, the PCM will command the EBTCM via serial data (CKT 800) to turn OFF traction control, and the EBTCM will illuminate the TRACTION OFF lamp.
• The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.
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 Clear Information function or by disconnecting the PCM battery feed.
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions:
• Poor connection at PCM - Inspect harness connectors for the following items:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connections
• 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 ICM. A change in voltage will indicate the location of the fault.
• Faulty Ignition Coil Remove the ignition coils and inspect the ignition control module and coils for cracks, carbon tracking, or other signs that indicate that the coil secondary circuit is arcing to the ICM or ICM wiring harness. Refer to
Ignition Control Module Replacement .
• Secondary ignition wire(s) arcing to wiring harness. Check secondary ignition wires for carbon tracking or other signs of damage.
Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
- 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.
DTC P1374 3X Reference Circuit
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