P0340
PowertrainCamshaft Position Sensor "A" Circuit Malfunction
The camshaft position sensor circuit has a fault. The ECU isn't getting a usable signal from the sensor that tracks where the camshaft is in its rotation.
ⓘ Information only. This page provides general educational information about fault code P0340. 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 P0340 mean?
P0340 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Camshaft Position Sensor "A" Circuit Malfunction.
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:
- • Engine warning light
- • Hard or no starting in some cases
- • Stalling, especially when warm or at idle
- • Misfires across multiple cylinders
- • Power loss and reduced throttle response
- • Sometimes a 'no spark' or 'no injection' condition
Possible causes
Causes commonly associated with P0340, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed cam position sensor (most common, sensors do wear out)
- 2. Damaged sensor connector, often from heat or oil contamination
- 3. Wiring damage between sensor and ECU
- 4. Oil leak fouling the sensor, the cam sensor often sits where rocker cover gaskets leak onto it
- 5. Damaged or worn cam sensor reluctor wheel (the toothed ring the sensor reads)
- 6. On chain-prone engines, related to timing chain stretch (sensor reads cam position incorrectly because chain is out)
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. Visual inspect the sensor and its connector. Oil saturation is extremely common, often from a leaking cam cover gasket. Sensor will need replacing once oil-contaminated
- 2. Resistance-test the sensor against the manufacturer's spec
- 3. Check live data for cam position signal, no signal at cranking confirms the sensor or wiring is the issue
- 4. On cars known for timing chain stretch (BMW N47, Ford EcoBoost, VAG TFSI), check whether P0016/P0017 are also stored, that points to chain rather than sensor
Common questions about P0340
Will the car start with this code? +
Sometimes, sometimes not. Modern engines need both crank and cam signals to know how to fire injectors and ignition. With a partial signal the engine might start but run poorly; with a fully open circuit it usually won't start at all.
Could this be the timing chain? +
Possibly, on engines known for timing chain stretch. If you have P0340 alongside P0016 or P0017 on a BMW N47 or similar, the underlying issue is more likely the chain than the sensor. A new sensor won't fix a stretched chain.
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 →