P2641Torque Management Feedback Signal B
- Generic OBD-II code · Powertrain
- Can trigger limp mode
- How the car detects it
- On Allison automatics, feedback B belongs to Low Range Torque Protection (LRTP): in the low ranges the TCM caps engine torque to spare gears and output shaft and checks that the engine respects the cap. P2641 sets when the engine reports more torque than permitted. Allison bulletin TT7401EN describes 2013 Cummins ISX12 engines with 4700/4800 transmissions: at idle in Low Reverse the ECM broadcast a wrong torque value, CHECK TRANS came on and Low Reverse was blocked until the ECM received calibration PH9.30.0.6 or later. Mack and Volvo tech tip TT-013-2015 sees the code under heavy load without drivability effects and also prescribes newer engine software. Navistar names it for Allison 1000/2000 calibrations. P2637 is the counterpart for request A.
- What you may notice
- CHECK TRANS lamp on
- Low Reverse or other low ranges unavailable
- Code appears under high load, often without noticeable drivability change
- Likely causes
- LikelyEngine ECM software below the level required for the transmission (Cummins, Mack, Volvo)
- PossibleEngine broadcasts torque above the low-range limit requested by the TCM
- RareTransmission calibration not matched to the engine
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.