P2789Clutch A Adaptive Learning at Limit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check Transmission or warning lamp on
- Engine flare or slip during upshifts
- Harsh or delayed engagement of the affected clutch
- Likely causes
- LikelyOutdated transmission calibration needing a reflash
- PossibleEngine reports torque inaccurately, so clutch adaptation drifts
- PossibleWorn clutch plates or leaking clutch piston seals
- RareDegraded fluid or a sluggish pressure control solenoid
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.