P0391Camshaft Position Sensor B Circuit Range/Performance Bank 2
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- Camshaft position sensor B is the exhaust camshaft sensor; bank 2 is the side without cylinder 1, so the code only occurs on V and boxer engines with one exhaust cam sensor per bank. P0391 means the bank 2 exhaust cam signal is present, but the number or position of its pulses does not fit the crankshaft. GM's 3.0 twin-turbo V6 (LGW) expects 4 to 6 pulses in the first 12 reference events and 398 to 402 per 100 engine cycles on the four-tooth wheel, after two trips; the Saab 9-4X 2.8 turbo V6 (LAU) checks pulses per crank revolution below 2,520 rpm. The 2004 Northstar requires each edge within a window of crank teeth, and GM's 2004 3.6-litre V6 (LY7) counts implausible signals over two drive cycles. The phaser then goes to its base position and the engine cranks longer. Mechanical causes – damaged tone wheel, jumped chain – matter more here than with P0390.
- What you may notice
- Check engine light on
- Loss of power (bank 2 exhaust cam timing in its base position)
- Longer cranking
- Rough idle
- Occasional stalling
- Likely causes
- LikelyTone wheel on the bank 2 exhaust phaser damaged, loose or wrongly fitted
- PossibleInterference or loose contact producing extra edges
- PossibleSensor loose, wrong O-ring or gap, chips on the magnet
- PossibleTiming chain stretched or jumped
- PossibleSensor faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €60 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.