Powertrain, generic (extended)

P2644 Torque Management Feedback Signal B High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P2644 reports that torque management feedback B exceeds its upper range limit. No manufacturer publishes a code-specific description. The closest documented case is Allison's P2641: a 2013 Cummins ISX12 calibration reported more torque than the low-range cap allowed, and Mack and Volvo trucks showed the same code under heavy load until the engine software was updated. A reading that is not just above the cap but beyond any valid value points to the same family of problems, namely engine software that scales or encodes the torque message differently from what the transmission expects, or a wired signal shorted to voltage. Low ranges may be locked out and the warning lamp lit. P2643 is the low fault, P2640 the high fault of signal A.

Likely causes

Engine software sends torque with a scaling the transmission does not expect
Engine calibration older than the level required by the transmission maker
Wired feedback line shorted to voltage

Symptoms

  • Transmission warning lamp on
  • Low ranges blocked
  • Shift quality reduced

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–500
Time0.5–2.5 h

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

Parts involved

tcmcommunication bus

Related codes

P2641P2642P2643P2640

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