Crankshaft Position Sensor A Circuit Intermittent
The P0339 code indicates that the Powertrain Control Module (PCM) has detected an intermittent, erratic, or missing signal from the crankshaft position sensor 'A' circuit. The PCM relies on this critical signal to determine engine RPM and crankshaft position for proper fuel injection and ignition timing, setting this code when the signal drops out unexpectedly.
This code is highly urgent because an intermittent crankshaft position signal can cause the engine to stall unexpectedly while driving or fail to start. It poses a significant safety risk and can leave you stranded.
Common symptoms
- Illuminated Check Engine Light
- Engine stalling or dying unexpectedly while driving
- Engine cranks but will not start (no-start condition)
- Rough idling, misfires, or hesitation during acceleration
- Tachometer drops to zero or behaves erratically while the engine is running
Likely causes
- Faulty or failing crankshaft position sensor
- Loose, corroded, or damaged wiring and connectors in the sensor circuit
- Excessive debris or metal shavings on the magnetic tip of the sensor
- Damaged or missing teeth on the crankshaft reluctor ring (tone ring)
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Perform a visual inspection of the sensor's wiring harness and connector.
Look for: Look for frayed wires, melted insulation, or a loose, backed-out, or corroded connector at the sensor.
Remove the crankshaft position sensor and inspect it physically.
Look for: Look for metal shavings, heavy oil contamination, or physical damage on the magnetic tip of the sensor that could disrupt the signal.
Inspect the crankshaft reluctor ring (tone ring).
Look for: Look through the sensor mounting hole while turning the engine by hand to check for missing, bent, or damaged teeth on the ring.
Test the sensor's circuit for proper reference voltage and ground.
Look for: Using a multimeter, verify that the sensor is receiving the correct reference voltage (usually 5V or 12V) and has a solid ground according to the manufacturer's wiring diagram.
Monitor the sensor signal output using an oscilloscope.
Look for: Look for a clean, consistent square wave (Hall effect) or AC sine wave (VR sensor) without dropouts, erratic spikes, or missing pulses while the engine is running or cranking.
This page explains the generic P0339 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.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.