Powertrain, generic (extended)

P2391 Diesel Intake Air Flow B Control Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Soot and oil deposits making the B flap stiff
Worn plastic gears or shaft bearing in the throttle unit
Weak motor or high resistance in the drive circuit
Position sensor reporting an offset angle

Symptoms

  • MIL on
  • Regeneration of the particulate filter does not complete
  • Occasionally reduced power or uneven response

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–600
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

diesel intake throttle valvethrottle valve motoractuator wiring

Related codes

P2394P2395P2397P239BP02E1

References: law.cornell.edu, gsi.ext.gm.com, ms-motorservice.com.