GMC Code P1377 – 4X Reference Pulse Ignition Control Module Camshaft Reference Pulse Incorrect

GMC P1377 Code Description

The GMC P1377 code indicates a problem with the vehicle’s Ignition Control Module (ICM). Specifically, it points to an issue where the signal from the Camshaft Position Sensor (CMP) to the 4X reference signal is incorrect. The CMP sensor is responsible for detecting the position of the camshaft relative to the crankshaft, while the 4X reference signal provides a timing reference for the ignition system.

Common Causes of GMC P1377

NOTE: The listed causes may not be a complete list of all potential issues, and there could be other causes.

1. Faulty Camshaft Position Sensor: A defective CMP sensor may send incorrect signals to the ICM.
2. Wiring Issues: Damaged or corroded wiring connecting the sensors to the ICM can lead to signal discrepancies.
3. Faulty Ignition Control Module: If the ICM is defective, it may not be able to correctly interpret the signals from the sensors.
4. Engine Timing Chain/Belt Problems: Issues with the timing chain or belt can affect the synchronization of the camshaft and crankshaft.

Symptoms of GMC P1377

1. Irregular Idle or Stalling: The engine may struggle to maintain a consistent idle speed or may even stall completely.
2. Misfires: Irregular ignition of cylinders can result in power loss and rough operation.
3. Decreased Fuel Efficiency: The engine may consume more fuel than usual due to inefficient combustion.
4. Check Engine Light On: The GMC P1377 code will trigger the check engine light to alert the driver of the issue.

How to Fix GMC P1377 Code

1. Diagnose the Problem: Use a diagnostic scanner to retrieve the error code and perform additional tests to identify the exact cause of the issue.
2. Replace the Camshaft Position Sensor: If the sensor is faulty, it will need to be replaced to ensure accurate signal transmission.
3. Check and Repair Wiring: Inspect the wiring harness for any damage or corrosion and repair or replace as necessary.
4. Replace the Ignition Control Module: If the ICM is found to be defective, it will need to be replaced to restore proper operation.
5. Reset the Error Code: After completing the repairs, clear the code from the vehicle’s computer to reset the check engine light.