The P0337 diagnostic trouble code (DTC) indicates a problem with the crankshaft position sensor (CKP) circuit, specifically a low input voltage signal detected by the powertrain control module (PCM). This code is a generic powertrain code, applying to all OBD-II equipped vehicles, including models from various manufacturers like GM, Ford, Toyota, and Honda.
What Does the P0337 Code Mean?
The CKP sensor is vital for engine management, monitoring engine speed (RPM) and crankshaft position. This data is crucial for precise ignition timing and fuel delivery. The PCM uses the crankshaft’s position, relative to the camshaft(s), to calculate the optimal timing for spark ignition. Since the camshafts rotate at half the crankshaft’s speed, the PCM must differentiate between intake and exhaust strokes. The CKP and camshaft position (CMP) sensors provide input signals, a 5-volt reference, and a ground to the PCM. A low voltage signal from the CKP sensor triggers the P0337 code.
CKP sensors typically use electromagnetic, hall-effect technology. They are positioned close to a reluctor ring on the crankshaft. As the crankshaft rotates, the reluctor ring’s teeth interrupt the magnetic field, generating voltage fluctuations. The PCM interprets these fluctuations as a waveform, representing crankshaft position and speed. When the input voltage from the CKP sensor falls below the expected threshold, the P0337 code is stored, and the malfunction indicator lamp (MIL) might illuminate.
Severity and Symptoms of a P0337 Code
A P0337 code is considered severe and can prevent the engine from starting. Even if the engine runs, it might lead to drivability issues and a potential no-start condition later. Common symptoms include:
- No-Start Condition: The engine may crank but fail to start.
- Erratic Tachometer: The tachometer might not display RPM or show inaccurate readings.
- Hesitation/Stumbling: The engine might hesitate or stumble during acceleration.
- Poor Performance: Reduced engine power and overall performance.
- Decreased Fuel Efficiency: The engine might consume more fuel than usual.
Common Causes of a P0337 Code
Several factors can contribute to a P0337 code:
- Faulty CKP Sensor: A malfunctioning CKP sensor is the most common cause.
- Wiring Issues: Open or shorted wiring in the CKP sensor circuit can disrupt the signal.
- Connector Problems: Corroded or damaged connectors at the CKP sensor can impede signal transmission.
- PCM Malfunction: A faulty PCM or programming error can misinterpret sensor data.
- Damaged Reluctor Ring: A damaged or missing reluctor ring can disrupt the signal generation.
Diagnosing and Repairing a P0337 Code
Diagnosing a P0337 code requires a diagnostic scanner, a digital volt/ohmmeter (DVOM), and an oscilloscope.
- Visual Inspection: Begin by inspecting wiring harnesses and connectors for damage, corrosion, or fluid contamination.
- Retrieve Codes: Connect the scanner and retrieve stored codes and freeze frame data.
- Voltage Test: Check the voltage at the CKP sensor connector. Verify the presence of a 5-volt reference, a ground signal, and output signal(s) (consult manufacturer specifications).
- Sensor Resistance Test: Disconnect the CKP sensor and test its resistance using the DVOM, comparing the readings to manufacturer specifications. Replace the sensor if the resistance is out of range.
- Waveform Analysis: Use an oscilloscope to analyze the waveform pattern of the CKP sensor signal. Look for irregularities like spikes, glitches, or missing voltage blocks. Wiggle the wiring harness to identify loose connections.
- Circuit Continuity: If the waveform at the sensor differs from the waveform near the PCM, test circuit continuity between the sensor and the PCM using the DVOM. Repair or replace any open or shorted circuits.
- PCM Check: If all other components check out, suspect a faulty PCM or a programming error.
Remember to consult manufacturer-specific repair information and technical service bulletins (TSBs) for detailed diagnostic procedures and wiring diagrams. Replacing the CKP and CMP sensors as a set is sometimes recommended.
