P0391: Camshaft Position Sensor "B" Circuit Range/Performance (Bank 2)
The bank 2 camshaft position sensor B signal does not fit the crankshaft signal.
Normal risk
Usually drivable, but the engine may start hard or run poorly. Have it checked soon.
Short answer · Can I keep driving with P0391?
Usually yes, but starting may take longer and variable valve timing may be switched off, so power can drop. Have it checked soon.
What does P0391 mean?
Code P0391 means the signal from camshaft sensor B on bank 2 is present but does not fit the crankshaft signal. A stretched timing chain or belt, a damaged sensor wheel or a faulty sensor can cause it. On most engines sensor B reads the exhaust camshaft. Bank 2 is the side of the engine without cylinder 1.
What the car does when the code is set
The check engine light comes on. Most engines keep running using the crankshaft signal, but starting may take longer, and the variable valve timing may be switched off, which reduces power.
How the system works
The camshaft turns at half the crankshaft speed, so the crankshaft signal alone cannot tell whether a piston at top dead centre is on its compression or exhaust stroke. The camshaft position sensor reads a trigger wheel on the camshaft and gives that information. The engine control unit uses it for sequential injection, ignition on some engines and variable valve timing control. Many engines can still run without it after a few revolutions, but starting may take longer.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Faulty camshaft position sensorThe sensor fails or gives an irregular signal.
- Wiring or connector faultOil leaks from the cam cover often reach the connector.
- Timing problemA stretched chain or jumped belt changes the signal timing.
- Damaged trigger wheelBent or broken teeth on the camshaft trigger.
How it is diagnosed
- Check the connectorLook for oil in the connector and damaged pins.
- Check the sensor signalCheck supply, ground and signal as in the service data.
- Check for related codesCombined with crankshaft-camshaft correlation codes, the timing should be checked.
- Replace and clearAfter replacing the sensor, clear the code and check the engine starts normally.
Questions about P0391
Can I swap the bank 1 and bank 2 sensors to test?
On many engines the sensors are the same part. Swapping them and checking whether the code moves to the other bank is a simple test; the service data confirms whether they are interchangeable.
Can I drive with a camshaft sensor code?
Usually yes, but the engine may be harder to start and use more fuel. Have it fixed soon.
Why do I need a timing check?
If both camshaft and crankshaft sensors are fine but codes persist, the timing itself may have shifted.