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DTC codes / GM codes / P1374

P1374 · GM3X Reference Circuit

P1374 on GM vehicles indicates that the ignition control module (ICM) is not receiving the expected 3X reference signal from the crankshaft position sensor, or the signal is erratic. The engine control module (ECM) monitors this circuit to determine engine speed and position for proper ignition timing and fuel delivery, and it sets the code when the 3X reference pulses are missing or incorrect.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Engine may stall or misfire, especially at idle or low speeds
  • Rough running or hesitation during acceleration
  • Hard starting or no-start condition
  • Illuminated check engine light (CEL) with P1374 stored
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Faulty crankshaft position sensor (CKP) or its wiring
  2. Damaged or corroded 3X reference circuit wiring (open, short, or high resistance)
  3. Failed ignition control module (ICM)
  4. Poor electrical connection at the ICM or ECM connectors
  5. Faulty ECM (rare)
  6. Mechanical issue such as a damaged reluctor ring or excessive timing chain slack

How to diagnose and fix it

  1. Inspect the crankshaft position sensor and its wiring for physical damage or corrosion
  2. Check the 3X reference circuit for continuity and shorts using a multimeter
  3. Test the ICM and its connections, including grounds and power feeds
  4. Verify the reluctor ring on the crankshaft for damage or debris
  5. Replace the crankshaft position sensor if faulty
  6. Replace the ignition control module if testing indicates failure
  7. Clear the code and perform a road test to confirm the repair

Before you replace the ignition module

  • A loose or corroded ground connection at the ICM can mimic a failed module and set P1374, so always check grounds first.
  • The 3X reference signal is often confused with the 18X or 24X signals; ensure you are testing the correct circuit for this code.
  • Intermittent P1374 can be caused by wiring chafing near hot exhaust components, which may not show up in a simple continuity test.
  • A failing crankshaft position sensor may not always set a CKP-specific code, so P1374 can be the only clue.
  • After replacing the ICM or CKP, a crankshaft variation learn procedure may be required on some GM models to prevent false codes.

Can I keep driving with P1374?

If the engine runs smoothly and the check engine light is steady, you can drive cautiously to a repair shop, but avoid heavy acceleration or long trips. If the engine stalls, misfires badly, or the light flashes, stop driving and have the vehicle towed to prevent damage.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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