Crankshaft Position Sensor A Circuit Low
Diagnostic trouble code P0337 indicates that the powertrain control module (PCM) has detected an abnormally low voltage signal from the crankshaft position sensor 'A' circuit. The PCM sets this code when the sensor's output voltage drops below the manufacturer's specified minimum threshold, preventing the computer from accurately determining engine RPM and crankshaft position.
This code is highly urgent because the crankshaft position sensor is critical for ignition and fuel timing. A failure here can cause the engine to stall while driving or refuse to start entirely, leaving you stranded.
Common symptoms
- Illuminated Check Engine Light
- Engine cranks but will not start
- Engine stalling while driving or idling
- Rough idling and engine misfires
- Hesitation or lack of power during acceleration
Likely causes
- Faulty crankshaft position sensor
- Short to ground in the sensor wiring harness
- Corroded, loose, or damaged sensor connector
- Damaged or missing teeth on the crankshaft reluctor ring
- Faulty Powertrain Control Module (PCM)
What to check before replacing parts
Visually inspect the crankshaft position sensor, wiring harness, and connector.
Look for: Look for melted wires, chafing, bare copper touching metal (short to ground), or heavy corrosion inside the connector pins.
Monitor engine RPM with a scan tool while cranking the engine.
Look for: If the scan tool shows 0 RPM while the engine is actively cranking, the PCM is not receiving a signal from the crankshaft sensor.
Test the sensor's reference voltage and ground circuits using a digital multimeter.
Look for: Verify that the sensor is receiving the correct reference voltage (typically 5V or 12V depending on the system) and has a solid ground; a missing voltage indicates a wiring or PCM issue.
Measure the sensor's signal output using an oscilloscope.
Look for: Look for a clean, consistent square wave (Hall effect) or AC sine wave (VR sensor) pattern; a flatline or heavily distorted waveform confirms a bad sensor or short.
Inspect the crankshaft reluctor ring (tone ring) for physical damage.
Look for: Check for broken, bent, or missing teeth, as well as excessive debris buildup that could disrupt the magnetic field required for the sensor to generate a proper voltage signal.
This page explains the generic P0337 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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