P27A1 code meaning
Electric/Auxiliary Transmission Fluid Pump A Stuck On
Powertrain system Generic code P27xx codes Check engine light
What P27A1 means
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.
P27A1 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P27A1
- Pump hum from the gearbox after the engine or ignition is off
- 12 V battery discharged after standing
- Stop-start disabled and warning shown
Common causes of P27A1
- Most likelyHigh-side driver or pump relay stays closed
- PossiblePump control or enable line shorted to battery voltage
- PossibleIntegrated pump electronics ignore the off command
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aux trans pump aControl moduleWiring harness
What each part of P27A1 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 7 | Area: transmission. |
| A1 | The exact fault in that area. |
What to do next
- Note P27A1 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P27A1
What does P27A1 mean?
P27A1 means "Electric/Auxiliary Transmission Fluid Pump A Stuck On". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P27A1?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P27A1 fail an emissions test?
P27A1 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P27A1 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P27A1 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.