P0366
PowertrainCamshaft Position Sensor "B" Circuit Range/Performance (Bank 1)
Camshaft position sensor B on bank 1 is feeding the ECM a signal that doesn't line up with what the engine is actually doing, so the timing reference is off. On engines with variable valve timing this sensor tracks the second camshaft (often the exhaust cam), and when its reading drifts out of range the ECM can't trust it to coordinate fuelling and spark properly. For you that usually shows up as rough running and a warning light, and it's the kind of fault that's worth sorting before it turns into misfires.
ⓘ Information only. This page provides general educational information about fault code P0366. 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 P0366 mean?
P0366 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Camshaft Position Sensor "B" Circuit Range/Performance (Bank 1).
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 on, sometimes the only thing you'll notice early on
- • Lumpy idle that won't settle, occasionally dropping low enough to feel like it might stall
- • Flat spots and hesitation when you put your foot down, worse under load
- • Long cranking before it catches, particularly on a hot restart
- • Random misfires that come and go rather than sitting on one cylinder
- • Fuel economy creeping up on the motorway because the timing is being guessed at
Possible causes
Causes commonly associated with P0366, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. The camshaft sensor itself worn or breaking down internally. These sensors live in a hot, oily environment and lose accuracy with age, so it's the first suspect
- 2. Wiring or connector trouble at the sensor. Chafed insulation, green corrosion in the plug, or a connector that's worked loose will throw the signal out
- 3. Oil contamination round the sensor or in the connector, often from a leaking cam cover gasket weeping onto the plug
- 4. Worn or stretched timing chain letting the cam drift out of phase with the crank, common on higher-mileage chain-driven engines
- 5. A VVT or cam phaser fault, where the phaser isn't moving the cam where the ECM commanded it
- 6. Low oil level or poor oil pressure starving the phaser, which then reports a position the ECM rejects
- 7. Damaged reluctor ring with a chipped or missing tooth on the cam trigger wheel
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. Pull all the codes and look at live cam and crank data together. If a crank sensor or other cam codes (P0340 family) are stored alongside, chase those first because they change the picture
- 2. Get eyes on the sensor and its plug. Check for oil sitting in the connector, corroded pins, and a loom that's been rubbing on something. Half of these jobs end here
- 3. With the ignition on, check the reference voltage at the sensor connector, you're looking for roughly 5V give or take half a volt. No reference means a wiring or ECM supply problem, not a sensor
- 4. Measure the sensor resistance between signal and ground and compare it against the manual figure, often somewhere around 1 to 2 kΩ on the inductive type
- 5. Run a continuity check on the power, ground and signal wires back to the ECM, looking for an open or a short before you spend money on a new sensor
- 6. Clear it, drive it, and see how the fault returns. Comes straight back hard means a live fault. Intermittent points you at wiring or a marginal connector
Common questions about P0366
If I just clear the code, will it stay gone? +
If the sensor or its wiring is on the way out, clearing it only buys you a few miles before it returns, sometimes within the same drive. The ECM is reading the cam in real time, so a genuine fault will trip it again as soon as the engine is running. The only time clearing it sticks is when something knocked the code in as a one-off, like a temporary bad connection that's since reseated, and that's not common. If it comes back fast, stop resetting it and diagnose it properly.
What am I risking if I just leave it? +
The engine often drops into limp mode and runs on a default timing map, which protects it but leaves you with sluggish, lumpy performance. The real danger is the misfires that can come with bad cam timing. Dumping raw fuel into a hot catalytic converter cooks it, and a cat is far dearer than the sensor causing all this. Left long enough on a chain-driven engine, an ignored timing fault can mask a stretching chain that eventually does serious damage.
How quickly do I need to deal with it? +
It's not a roadside emergency if the car still drives, but don't sit on it for weeks. A faint or fault-coded sensor is one thing, but the moment you feel misfiring or the car going into limp mode you want it looked at within a few days to keep that cat safe. If it's only the warning light with no driveability change, you've got a little more breathing room, though you still want it diagnosed before the next MOT.
Is it the sensor itself or the wiring behind it? +
Could be either, and that's exactly why people waste money fitting a new sensor that doesn't fix it. Plenty of P0366s come down to oil-soaked connectors or chafed wiring rather than a dead sensor, especially on engines with a known cam cover oil leak. Check the reference voltage and the connector before you buy parts. If you've already fitted a new sensor and the code is still there, the fault is almost certainly in the loom, the timing chain, or the phaser, not the part you just replaced.
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 →