Powertrain, generic (extended)

P2642 Torque Management Feedback Signal B Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P2642 means feedback signal B arrives and lies inside its valid range, yet its value makes no sense for the current operating state, for example a torque figure that drifts away from what a limited request should produce or that changes implausibly fast. No manufacturer explains P2642 publicly. Allison ties request B to its low-range torque cap (LRTP) and logs the general code P2641 when the engine exceeds the cap; Honda documents the matching plausibility check for request A as P2638 on its nine-speed automatic and fixed false triggers with software and an idle relearn. By analogy, look first at engine and transmission software levels, then at the idle learn and at sensors feeding the torque model. Shifts may feel rough and low ranges can be restricted.

Likely causes

Engine and transmission software versions do not match
Idle or torque adaptation not learned after service
Faulty input to the engine torque model (air mass, intake air temperature)

Symptoms

  • Rough or delayed shifts
  • Transmission warning lamp on
  • Low ranges restricted

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

tcmecmcommunication bus

Related codes

P2641P2643P2644P2638

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