Code P1397 GMC: Understanding and Resolving the Camshaft/Crankshaft Timing Problem

The error code P1397 GMC is a generic OBD2 standard code that indicates a timing problem between the Camshaft Position Sensor (CMP) and the Crankshaft Position Sensor (CKP). In GMC vehicles, this desynchronization can lead to engine performance issues, power loss, and even starting difficulties. Understanding the causes, symptoms, and solutions for this code is essential for any owner or mechanic looking to keep their GMC pickup or SUV in perfect working order. This code is often associated with a range of models including the Sierra, Yukon, Acadia, and Canyon, among others.

Symptoms of Code P1397 on a GMC Vehicle

When the onboard computer (ECM) detects an abnormal discrepancy in the signals from the two sensors, it records the P1397 GMC code and illuminates the Malfunction Indicator Lamp (MIL) on the dashboard. The most commonly observed symptoms are:

• Engine cranks but won’t start: The vehicle has difficulty starting; it may crank for a long time without firing up.
• Unstable idle and rough idle: The engine shakes and its RPM fluctuates abnormally when stationary.
• Noticeable power loss: The vehicle lacks responsiveness and struggles to accelerate, especially under load.
• Increased fuel consumption: The ECU, not receiving the correct information, can no longer optimize the air-fuel mixture.
• Engine cut-out or stalling: In the most severe cases, the engine may stall suddenly.

Main Causes of Code P1397

Several elements can be the source of this error code. Precise diagnosis is necessary to avoid replacing parts unnecessarily.

• Mechanical timing problem: The timing belt or timing chain may have jumped one or more teeth, physically desynchronizing the camshaft and crankshaft.
• Sensor failure: The Camshaft Position Sensor (CMP) or the Crankshaft Position Sensor (CKP) is faulty, dirty, or has a faulty electrical circuit (cut wires, oxidized connector).
• Incorrect distance between the sensor and its trigger: The air gap (the clearance) between the sensor and the reluctor ring (the metal trigger) is not correct.
• Starter problem: A weak starter that turns the engine over too slowly can prevent the ECM from reading the signals correctly during startup.

Diagnostic Procedure and Solutions

To effectively diagnose a P1397 GMC code, it is recommended to follow a logical procedure.

Step 1: Visual Inspection
Start with a thorough inspection of the wiring and connectors of both sensors (CMP and CKP). Look for signs of wear, burning, corrosion, or loose wires.

Step 2: Checking signals with a diagnostic tool
Using an advanced OBD2 scanner or an oscilloscope, observe the signals from both sensors in real-time. A weak, irregular, or missing signal from one of the two sensors will confirm its failure.

Step 3: Checking mechanical timing
If the sensors and their wiring seem good, it is imperative to check the mechanical timing of the engine. This may require setting the engine to Top Dead Center (TDC) and verifying the alignment of the marks on the pulleys and engine block.

Possible solutions:

• Replace the faulty Camshaft Position Sensor (CMP) or Crankshaft Position Sensor (CKP).
• Repair or replace the damaged wiring harness.
• Clean the electrical connectors with contact cleaner.
• Adjust the sensor air gap if possible.
• Overhaul the timing system (belt/chain, tensioner, idler pulleys) if it is loose or has jumped teeth.

It is crucial to always clear the code after repairs and perform a road test to ensure the fault does not reappear. If the problem persists after replacing the sensors, a thorough check of the ECM may be necessary, although this is rarer.