P0391
Camshaft Position Sensor B Circuit Range/Performance Bank 2
Camshaft position
Generic OBD-II
High
What it means
P0391 means the bank 2 "B" camshaft position sensor signal is present but out of its expected range or inconsistent with the crankshaft signal. The ECM uses cam position for spark/fuel timing and variable valve timing, so this can cause hard starting, occasional stalling, rough running, and reduced power.
High
Can I keep driving? Drivable but unpredictable — it can cause hard starting, occasional stalling, or reduced power, so get it checked soon.
Common symptoms
What you'll notice
- Check-engine light on
- Hard starting
- Rough idle and reduced power
- Occasional stalling
Common causes
Most likely first
- Wiring or connector fault at the bank 2 'B' camshaft sensorLikely
- Faulty camshaft position sensor (bank 2, B)Common
- Timing-chain stretch or reluctor/tone-ring damage altering the signalCommon
- Oil contamination at the sensorLess often
- ECM fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and inspect the sensor connector and wiring.
- Compare the camshaft and crankshaft signals on a scope.
- Check for timing-chain stretch or tone-ring damage.
- Replace the camshaft sensor if it is out of spec.
- Address timing components if the cam/crank correlation is off. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0391?+
Short trips are usually okay, but stalling or a no-start can strand you, so have it fixed soon.
Can I just clear P0391?+
You can, but it returns until the sensor or its circuit is repaired.
Related codes
Often seen with P0391
Read & clear P0391 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX