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What is GM code P0337?

Published in Engine Diagnostic Codes 4 mins read

GM code P0337 signifies "Crankshaft Position Sensor 'A' Circuit Low." This diagnostic trouble code (DTC) is logged by the Powertrain Control Module (PCM) when it detects an abnormally low voltage signal from the crankshaft position (CKP) sensor's "A" circuit. Essentially, the vehicle's computer isn't receiving the expected electrical signal from the sensor responsible for monitoring the crankshaft's rotation.

Understanding the Crankshaft Position Sensor (CKP)

The crankshaft position sensor is a vital component in modern vehicle engines. It plays a crucial role in engine management by:

  • Monitoring Engine Speed: It detects the rotational speed of the crankshaft.
  • Determining Piston Position: It helps the PCM identify the exact position of the pistons within the cylinders.
  • Timing Fuel Injection and Ignition: This information is critical for the PCM to accurately time fuel injection and ignition spark, ensuring optimal engine performance and efficiency.

When the PCM detects a "Circuit Low" condition, it indicates that the voltage signal from the sensor is below the expected operational threshold, suggesting a problem with the sensor itself or its associated wiring.

Why P0337 is Set

The PCM relies on precise signals from the CKP sensor to ensure the engine runs smoothly. If the signal from the "A" circuit drops too low, it disrupts the PCM's ability to accurately determine engine speed and position. This can lead to various drivability issues, as the PCM can't properly manage fuel delivery and ignition timing.

Common Symptoms of P0337

When the P0337 code is triggered, drivers may experience several noticeable symptoms:

  • Illuminated Check Engine Light: This is often the first and most obvious indicator that a problem has been detected.
  • Difficulty Starting: The engine might crank but fail to start, or it may take a long time to turn over.
  • Engine Stalling: The engine could unexpectedly shut off while driving or idling.
  • Rough Idle: The engine might run erratically, shaking or vibrating more than usual.
  • Reduced Engine Performance: You might notice a lack of power, hesitation during acceleration, or misfires.
  • Erratic Tachometer Readings: The RPM gauge may jump around or show incorrect readings.

Common Causes of P0337

Identifying the root cause of a P0337 code is crucial for proper diagnosis and repair. The common causes include:

Cause Explanation
Faulty Crankshaft Position Sensor The sensor itself can fail over time due to wear, heat exposure, or internal electronic issues, leading to an incorrect or absent signal.
Wiring Issues Problems with the wiring harness connected to the CKP sensor are frequent culprits. This can include:
- Chafed or Damaged Wires: Wires that are worn through their insulation, exposing the conductors.
- Corroded Connectors: Rust or debris on the electrical terminals preventing a proper connection.
- Open or Short Circuits: A break in the wiring (open circuit) or wires touching each other or ground (short circuit) affecting voltage flow.
Faulty Powertrain Control Module (PCM) While less common, a malfunctioning PCM can sometimes be the cause. The PCM might fail to properly interpret the sensor's signal or have internal faults.

Diagnosing and Addressing P0337

Addressing a P0337 code typically involves a diagnostic process to pinpoint the exact issue:

  • Visual Inspection: Mechanics will often start by visually inspecting the CKP sensor and its wiring for any obvious signs of damage, corrosion, or loose connections.
  • Wiring Continuity and Resistance Checks: Using a multimeter, technicians can test the continuity of the sensor's wiring and check for proper resistance to ensure the circuit is intact and not shorted.
  • Sensor Testing: The CKP sensor itself can be tested for proper voltage output and signal pattern, often using an oscilloscope to analyze its waveform.
  • Checking for Related Codes: Other diagnostic trouble codes might be present that could provide additional clues about the underlying problem.
  • PCM Diagnosis: If the sensor and wiring are confirmed to be in good working order, the PCM's functionality would then be assessed.

Depending on the diagnosis, solutions typically involve replacing the faulty crankshaft position sensor, repairing or replacing damaged wiring and connectors, or, in rare cases, replacing the PCM.