P277A code meaning
Electric/Auxiliary Transmission Fluid Pump B Hydraulic Leakage
Powertrain system Generic code P27xx codes Check engine light
What P277A means
P277A is not an electrical fault. The motor of auxiliary pump B runs, yet the oil it delivers escapes before pressure can build, so the module concludes that the hydraulic path around the pump leaks. Typical suspects are a damaged pump seal or O-ring, a check valve that does not close, worn bores in the valve body or a fluid level so low that the pump draws air. No manufacturer documents P277A publicly. How such a test can look is shown by GM's 2025 TCM tables for pump A on a CVT: during an engine auto-start the pump is commanded, and if both pulley pressure sensors stay under 200 kPa while more than 400 kPa is requested, a performance code follows. P0B0C is the leakage code for pump A. Without pressure, stop-start restarts may be harsh or disabled.
P277A at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairAfter a drive cycle
Symptoms of P277A
- Stop-start disabled or rough engine restarts
- Delayed drive engagement after standstill
- Warning lamp, possibly fluid traces under the gearbox
Common causes of P277A
- Most likelyDamaged pump seal or O-ring at the pump mounting
- PossibleLow transmission fluid level letting the pump draw air
- PossibleCheck valve in the pump circuit not sealing
- Less likelyWorn valve body bores causing internal leakage
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aux trans pump bHydraulic circuitValve body seals
What each part of P277A 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. |
| 7A | The exact fault in that area. |
What to do next
- Note P277A 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 P277A
What does P277A mean?
P277A means "Electric/Auxiliary Transmission Fluid Pump B Hydraulic Leakage". P277A is not an electrical fault. It is a generic code, so it means the same on every make.
Is it safe to drive with P277A?
Drive gently and only to a workshop. With P277A the car can go into limp mode (reduced power) to protect itself.
Will P277A fail an emissions test?
P277A 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 P277A to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will P277A clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.