Powertrain, generic (extended)

P28EE Electric/Auxiliary Transmission Fluid Pump B Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P28EE is the reverse of P28ED: electric transmission fluid pump B does not reach the speed its controller asks for. The motor is fed, but something holds it back, such as very cold and thick fluid, a binding or worn pump, debris in the gears or a low supply voltage. When the speed falls to zero the matching code is the stall P277C rather than this one. No manufacturer documents P28EE publicly. Comparable logic exists for single pumps: on the 2016 Cadillac ELR GM sets P1E3A, Type A, when commanded minus actual speed exceeds 200 rpm while more than 6.8 Nm is requested, while under P0B0D Ford's 2019 plug-in hybrids react to a speed under 95 percent of command for 3 s. CARB requires functional checks. The car then keeps the engine running or limits electric driving.

Likely causes

Pump binding, worn or contaminated with debris
Very cold, aged or wrong transmission fluid
Low supply voltage or high resistance in the pump feed

Symptoms

  • Transmission warning or check engine light on
  • Engine keeps running at stops, electric driving limited
  • Delayed engagement after an automatic engine restart

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,500
Time0.5–4 h

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

Parts involved

aux transmission pump btransmission fluid

Related codes

P28EDP277CP27A3P276D

References: gsi.ext.gm.com, fordservicecontent.com, law.cornell.edu.