Powertrain, generic (extended)

P27E1 Electric/Auxiliary Transmission Fluid Pump A Pressure Too Low

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

P27E1 is a hydraulic verdict, not a wiring one: electric auxiliary pump A was running on command, yet the pressure it built stayed below what the module expected. No manufacturer documents this exact code publicly. GM shows how such a check works on its CVTs (2025 TCM tables): during an engine auto-start, with more than 400 kPa requested, both pulley pressure sensors reading under 200 kPa for over 0.525 s set the broader performance code P2797, Type B. Wiring faults on the pump belong to P2796 and its siblings, leakage to P0B0C, and pump B has P27E2. Worn pump gears, a clogged intake screen, low fluid or a leaking check valve are typical. Stop-start is usually blocked, and restarts after a stop may engage harshly.

Likely causes

Worn pump gears or internal leakage inside pump A

Low or aerated transmission fluid, pump draws air

Intake screen of the pump partly blocked by debris

Check valve in the pump circuit not sealing

Symptoms

Stop-start function disabled
Jerky or delayed engagement when the engine restarts after a stop
MIL or transmission warning lit

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–2,000

Time1–6 h

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

Parts involved

aux transmission pump atransmission fluidvalve body

Related codes

P27E2 P2797 P0B0C P2796 P27E3

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.