Powertrain, generic (extended)

P2640 Torque Management Feedback Signal A High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Engine ECM software reports torque values the transmission calibration does not accept
Outdated or wrong transmission controller calibration
Hard-wired feedback line shorted to voltage (where used)

Symptoms

  • Check transmission lamp or MIL on, depending on calibration
  • Firm or abrupt upshifts
  • Torque reduction during shifts no longer active

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–600
Time0.5–2.5 h

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

Parts involved

tcmcommunication bus

Related codes

P2637P2638P2639P2644P0614

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