P277A
Electric/Auxiliary Transmission Fluid Pump B Hydraulic Leakage
The second auxiliary transmission fluid pump cannot maintain pressure even at high duty cycle. Indicates internal hydraulic leakage downstream of the pump.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Common causes
Ordered by how often each turns out to be the cause.
- Worn or hardened seals downstream of pumpCommon
- Pressure relief or bypass valve stuck openPossible
Parts involved
- Aux Trans Pump B
- Hydraulic Circuit
- Valve Body Seals
P277A is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.