P2391Diesel Intake Air Flow B Control Performance
- 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
- P2391 compares where the B intake throttle should be with where its position sensor says it is. If the gap stays too large under a steady command, the module concludes that the flap is sluggish or obstructed, typically by soot and oil deposits from EGR and crankcase gases, a worn gear stage or a weak motor. No published manufacturer table covers P2391. GM's 2025 diesels judge the A valve (P02E1) on a tracking error above 10 % in 960 of 1,200 samples at 6.25 ms, only once coolant has reached 40 °C and outside the cold-start strategy, and light the MIL in the first trip. Unlike the stuck codes P2394 and P2395, this one does not say in which direction the flap lags. Expect higher NOx, possibly blocked regeneration and sometimes reduced power.
- What you may notice
- MIL on
- Regeneration of the particulate filter does not complete
- Occasionally reduced power or uneven response
- Likely causes
- LikelySoot and oil deposits making the B flap stiff
- PossibleWorn plastic gears or shaft bearing in the throttle unit
- PossibleWeak motor or high resistance in the drive circuit
- RarePosition sensor reporting an offset angle
- 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: €50 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.