P2641 code meaning
Torque Management Feedback Signal B
What P2641 means
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.
P2641 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2641
- CHECK TRANS lamp on
- Low Reverse or other low ranges unavailable
- Code appears under high load, often without noticeable drivability change
Common causes of P2641
- Most 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
- Less likelyTransmission calibration not matched to the engine
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
TCMECMCommunication bus
What each part of P2641 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 6 | Area: computer (engine control module) and output circuits. |
| 41 | The exact fault in that area. |
What to do next
- Note P2641 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 P2641
What does P2641 mean?
P2641 means "Torque Management Feedback Signal B". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P2641?
Drive gently and only to a workshop. With P2641 the car can go into limp mode (reduced power) to protect itself.
Will P2641 fail an emissions test?
P2641 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P2641 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will P2641 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.