P27A1Electric/Auxiliary Transmission Fluid Pump A Stuck On
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- How the car detects it
- P27A1 means auxiliary transmission fluid pump A keeps running although the controller has not asked for it, or the module still sees current or rotation with the command off. Such electric pumps hold pressure in the gearbox while the engine rests during stop-start or hybrid operation. A pump that cannot be switched off usually points to a high-side driver or relay stuck closed, a control line shorted to battery voltage, or pump electronics that ignore the command. No manufacturer documents P27A1 publicly. Ford's 2024 summary for the 10R60/10R80 and 8F57 gearboxes shows that the smart pump returns its own speed and current, which is what makes an unwanted run visible; GM's 2025 tables watch the pump drivers for shorts (P2798, P2799). Expect extra battery drain and pump noise.
- What you may notice
- Pump hum from the gearbox after the engine or ignition is off
- 12 V battery discharged after standing
- Stop-start disabled and warning shown
- Likely causes
- LikelyHigh-side driver or pump relay stays closed
- PossiblePump control or enable line shorted to battery voltage
- PossibleIntegrated pump electronics ignore the off command
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.