Powertrain, generic (extended)

P277B Electric/Auxiliary Transmission Fluid Pump B Driver Circuit Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P277B concerns the power stage that energises the motor of auxiliary pump B, wherever it sits: inside a separate pump controller or in the transmission module. The stage is switched on, but what comes back – current, speed or a status signal – does not fit the command, so the module rates the driver as implausible rather than reporting a plain open or short. No manufacturer documents P277B publicly. For pump A, Ford's 2024 OBD summary (10R60/10R80, 8F57) lists a related case: the pump flags implausible current together with implausible speed, stored as P0C29 (UDS P0C29_92). Overheated or failing driver electronics, a poor ground, low system voltage and a pump that loads the stage abnormally are the usual triggers. The gearbox then runs without the pump's support, which mainly affects stop-start.

Likely causes

Failing output stage in the pump controller or TCM
Poor ground or low system voltage at the driver
Pump motor loading the driver abnormally
Loose or corroded pins between driver and pump

Symptoms

  • Transmission warning or service message
  • Stop-start unavailable
  • Jerky drive-off after engine restarts

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,500
Time0.5–4 h

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

Parts involved

aux trans pump b drivercontrol module

Related codes

P0C29P277DP276FP276B

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