Powertrain, generic (extended)

P2789 Clutch A Adaptive Learning at Limit

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

P2789 says the controller has pushed its learned fill or pressure corrections for a clutch to the edge of the permitted window and still cannot reach the shift quality it aims for. The code is well documented by Allison for its 1000/2000 Series automatics, where it lights the Check Transmission lamp and the Prognostics view flags the affected clutch as not OK. Tech tip TT8008EN covers Thomas Built school buses whose natural-gas Cummins ISB engines report torque inaccurately, causing flares on the first two upshifts (C3/C4); TT7994 covers IC Bus models with a PSI 8.8 litre propane engine making more torque than expected (C3); SIL 34-1K2K-19 describes low-mileage units with C1 at its limit and calls for B191 or newer TCM software. In dual-clutch boxes P278F is the clutch B sibling.

Likely causes

Outdated transmission calibration needing a reflash
Engine reports torque inaccurately, so clutch adaptation drifts
Worn clutch plates or leaking clutch piston seals
Degraded fluid or a sluggish pressure control solenoid

Symptoms

  • Check Transmission or warning lamp on
  • Engine flare or slip during upshifts
  • Harsh or delayed engagement of the affected clutch

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–3,000
Time0.5–8 h

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

Parts involved

dual clutch atcm

Related codes

P278FP2788P2787

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.