P2640 code meaning
Torque Management Feedback Signal A High
What P2640 means
P2640 is the high-range fault of torque management feedback signal A: the confirmation that the transmission controller receives after asking the engine for a torque change carries a value above the plausible upper limit. On Allison-equipped trucks this feedback is not a separate wire but part of the engine data broadcast on the J1939 link, so a high reading usually means the engine claims more torque than is physically possible or than was requested. No manufacturer documents P2640 publicly. For the related P2637 Cummins cured the fault with new ECM calibrations, a hint that software mismatches are a frequent root. P2637, P2638 and P2639 cover the general, plausibility and low faults of signal A. Expect harsher shifts and torque reductions that no longer work.
P2640 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2640
- Check transmission lamp or MIL on, depending on calibration
- Firm or abrupt upshifts
- Torque reduction during shifts no longer active
Common causes of P2640
- Most likelyEngine ECM software reports torque values the transmission calibration does not accept
- PossibleOutdated or wrong transmission controller calibration
- Less likelyHard-wired feedback line shorted to voltage (where used)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
TCMCommunication bus
What each part of P2640 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. |
| 40 | The exact fault in that area. |
What to do next
- Note P2640 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 P2640
What does P2640 mean?
P2640 means "Torque Management Feedback Signal A High". P2640 is the high-range fault of torque management feedback signal A: the confirmation that the transmission controller receives after asking the engine for a torque change carries a value above the plausible upper limit. It is a generic code, so it means the same on every make.
Is it safe to drive with P2640?
Drive gently and only to a workshop. With P2640 the car can go into limp mode (reduced power) to protect itself.
Will P2640 fail an emissions test?
P2640 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 P2640 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P2640 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.