P0338

What it means

P0338 means the engine control unit has detected a high signal condition in the crankshaft position sensor A circuit, as defined by SAE J2012. The unit saw a voltage or signal pattern from the sensor circuit that was above the expected range or a signal that was erratic, so it cannot reliably work out engine speed and crank position. Exact set conditions and how the sensor is wired vary by model and engine.

Symptoms

• Engine cranks but fails to start or is hard to start
• Engine stalls unexpectedly, often when warm
• Misfires, hesitation or rough running
• Rev counter flickers, drops to zero or does not work
• Engine management warning light on
• Loss of power or limp mode on some models

Possible causes

• Faulty crankshaft position sensor, internal fault or heat-related failurelikely
• Damaged, chafed or shorted wiring to the sensor, including a short to a voltage supplylikely
• Corroded, loose or contaminated connector terminals at the sensor or control unitlikely
• Damaged or contaminated reluctor wheel or tone ring, or metal debris on the sensor tippossible
• Incorrect sensor air gap or loose sensor mountingpossible
• Electrical interference from poor earths or faulty ignition componentspossible
• Fault within the engine control unitrare

How to diagnose

1. Read the stored and pending codes and the freeze frame data, noting engine speed, temperature and whether the fault was present at start-up or while running
2. Check for related codes such as camshaft position sensor or misfire codes that may point to a shared cause
3. Visually inspect the sensor, its wiring and connector for chafing, heat damage, oil contamination, corrosion or bent pins
4. Check the sensor is secure, undamaged and correctly seated, and look at its tip for metal debris
5. Inspect the reluctor wheel through the sensor aperture where possible for damage, missing teeth or debris
6. With the ignition on, test the sensor supply, signal and earth circuits against the manufacturer's data for shorts to voltage, open circuits and high resistance
7. View the sensor signal on an oscilloscope while cranking and running, looking for dropouts, noise or an abnormal pattern, and compare it with a known good waveform for that engine
8. Check the battery condition and engine and chassis earths, then only condemn the control unit once wiring and sensor are proven good

How to fix

• Replace the crankshaft position sensor if it fails testing, using the correct type for the engine
• Repair or replace damaged wiring, and clean or renew faulty connector terminals
• Remove debris and correct the mounting or air gap, replacing the sensor if it is damaged
• Repair or replace a damaged reluctor wheel or tone ring, following the model-specific procedure
• Restore poor battery or earth connections and cure any source of electrical interference
• Have the control unit tested, repaired or replaced, with any required programming, only if all else is proven good

Can I keep driving?

Nearby codes

• P0337GenericCrankshaft Position Sensor A Circuit Low
• P0339GenericCrankshaft Position Sensor A Circuit Intermittent