P0338
PowertrainCrankshaft Position Sensor A Circuit High Input
The ECU watches the crankshaft sensor signal to know exactly where the pistons are. When it sees the voltage from that circuit sitting too high, higher than it should ever read, it flags P0338. For you, the driver, that usually shows up as a car that's hard to start, stalls, or runs rough, because the engine has lost the timing reference it needs to fire properly.
ⓘ Information only. This page provides general educational information about fault code P0338. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0338 mean?
P0338 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Crankshaft Position Sensor A Circuit High Input.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Check engine light on, sometimes alongside a no-start or intermittent stall
- • Engine cranks but takes several attempts to catch, or won't start at all when warm
- • Stalling at idle or when you come to a stop, then restarting fine a minute later
- • Jerky, hesitant acceleration as the timing signal drops in and out
- • Rev counter needle flicking or dropping to zero while the engine is still running
- • Fuel economy noticeably worse on a regular commute
Possible causes
Causes commonly associated with P0338, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failing crankshaft sensor itself, the most common cause. The internals break down with heat and age, and a high-voltage reading often means the signal has gone open or intermittent
- 2. Wiring or connector fault in the sensor circuit, frequently from heat cycling near the block or chafing against a bracket
- 3. Oil contamination in the connector, common on engines with a leaking rear main or cam cover seal that lets oil track down the loom
- 4. Poor earth or a short to a voltage supply somewhere in the harness pulling the signal line high
- 5. Worn or damaged reluctor ring on the crank, which throws the signal off even with a perfect sensor
- 6. Charging system playing up, an overcharging alternator can push odd voltages into the circuit
- 7. Faulty ECU, rare, and only worth considering once everything else checks out clean
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the freeze-frame data with a scanner and note whether the fault landed during cranking, hot running, or cold starts. That tells you a lot about where to look
- 2. Unplug the sensor and check the connector for oil, corrosion, and pushed-back pins. A connector full of oil is a frequent culprit and a cheap fix
- 3. Back-probe the signal and supply wires with the ignition on, you're looking for the expected reference of around 5 volts, not a stuck-high reading
- 4. Watch the live sensor signal while cranking to see if the voltage exceeds the upper limit or drops out altogether
- 5. Measure the sensor resistance with a multimeter and compare against the manufacturer's figure for that engine
- 6. Inspect the reluctor ring through the sensor hole for chipped or damaged teeth before condemning anything electrical
Common questions about P0338
What am I likely to pay to sort this out? +
If it's just the sensor, an independent garage will usually charge between £80 and £200 fitted, depending on how buried it is. The part is often £30 to £90. A main dealer can easily double that on labour, particularly on engines where the inlet manifold or starter has to come off to reach it. If the fault turns out to be wiring or a contaminated connector, you might get away with a repair under £100, but diagnosing a flaky harness eats time and that's where the bill climbs.
How do I know if it's the sensor or the wiring on my own car? +
Pull the connector and look at it first. Oil tracking down the loom or green corrosion on the pins points at wiring rather than the sensor. If the connector is clean and dry, back-probe the signal wire while cranking. A reading stuck high regardless of engine speed usually means the sensor or its supply, whereas a signal that's fine until the engine warms up tends to be a heat-sensitive sensor breaking down. Damaged reluctor teeth are rarer but show up as a signal that's present yet erratic with no wiring fault.
Can I just clean the connector and replace the sensor myself? +
Often yes. Cleaning out an oily connector with contact cleaner and re-seating the pins fixes a fair few of these. If you're replacing the sensor, mark the old one's orientation and torque the new one properly, since an air gap that's too wide gives the same symptoms. The catch is access. On some engines it's a two-minute job, on others you're working blind around the starter or dropping a guard, so check where yours sits before committing.
Will clearing the code make it stay gone? +
Only if you've fixed what caused it. Clear P0338 on a dying sensor and it'll be back within a few starts, often as soon as the engine heats up again. If you cleaned a contaminated connector the fault may stay away for a while, but if the oil leak feeding it is still there it'll creep back. A code that returns quickly after a reset is your sign the underlying part hasn't actually been dealt with.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →