P0339

What it means

P0339 means the engine control unit has detected an intermittent fault in the crankshaft position sensor A circuit. The crankshaft signal drops out, becomes erratic or disappears briefly while the engine is turning, then returns. The control unit relies on this signal for engine speed, crank position and misfire detection, so any dropout can upset ignition and fuelling.

Symptoms

• Engine cuts out or stalls intermittently, often when warm
• Intermittent long cranking or no start
• Rough running, hesitation or misfire
• Rev counter dropping to zero or flickering while driving
• Engine warning light on, sometimes with stored misfire codes
• Loss of power or engine entering limp mode

Possible causes

• Loose, corroded or damaged connector at the crankshaft position sensorlikely
• Chafed, broken or heat-damaged wiring between the sensor and the control unit, including intermittent open circuit or shortlikely
• Failing crankshaft position sensor, often heat-sensitive and only faulty when hotlikely
• Damaged, dirty or contaminated reluctor wheel or trigger wheel, or metal debris on the sensor tippossible
• Incorrect sensor air gap or loose sensor mountingpossible
• Electrical interference or poor power or earth supply to the sensor or control unitpossible
• Fault within the engine control unitrare

How to diagnose

1. Read all stored and pending codes and note freeze frame data such as engine speed, temperature and load when the fault set; check for related camshaft or misfire codes.
2. Inspect the sensor connector and wiring along its length for chafing, oil contamination, heat damage, corrosion and poor terminal tension; wiggle the harness with the engine running and watch for rev signal dropouts.
3. Check the sensor is secure and undamaged, then remove it and inspect the tip for debris, damage or excessive wear.
4. Inspect the visible part of the reluctor wheel for damaged, missing or dirty teeth; the method of access depends on the model and engine.
5. Check the sensor supply voltage, signal and earth against the manufacturer's data for your model, as sensor type (inductive or Hall effect) varies.
6. Monitor live engine speed data while cranking and running, and compare with the camshaft signal, looking for dropouts or erratic readings.
7. Test the circuit for resistance, shorts and continuity between sensor and control unit with the battery disconnected, following the wiring diagram.
8. Check the battery condition and main earths, since low voltage during cranking can disturb the signal.

How to fix

• Clean, repair or replace the damaged connector or terminals at the sensor.
• Repair or replace the damaged section of wiring, avoiding joins that could fail later.
• Replace the crankshaft position sensor if it fails testing or is heat-sensitive, and ensure correct fitting and air gap where applicable.
• Clean the sensor tip, or repair or replace a damaged reluctor wheel as required by the engine design.
• Rectify poor battery, power or earth connections that disturb the signal.
• If all else is proven sound, investigate the control unit and repair or replace it as the manufacturer directs.

Can I keep driving?

Nearby codes

• P0338GenericCrankshaft Position Sensor A Circuit High
• P033AGenericKnock/Combustion Vibration Sensor D Circuit