P2391 code meaning
Diesel Intake Air Flow B Control Performance
Powertrain system Generic code P23xx codes Check engine light
What P2391 means
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.
P2391 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P2391
- MIL on
- Regeneration of the particulate filter does not complete
- Occasionally reduced power or uneven response
Common causes of P2391
- Most 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
- Less likelyPosition sensor reporting an offset angle
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Diesel intake throttle valveThrottle valve motorActuator wiring
What each part of P2391 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 3 | Area: ignition system or misfire. |
| 91 | The exact fault in that area. |
What to do next
- Note P2391 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2391
What does P2391 mean?
P2391 means "Diesel Intake Air Flow B Control Performance". P2391 compares where the B intake throttle should be with where its position sensor says it is. It is a generic code, so it means the same on every make.
Is it safe to drive with P2391?
Drive gently and only to a workshop. With P2391 the car can go into limp mode (reduced power) to protect itself.
Will P2391 fail an emissions test?
Yes, it can. P2391 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2391 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P2391 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.