P27A6
Electric/Auxiliary Transmission Fluid Pump B Stuck On
The second auxiliary transmission fluid pump runs even when no command is active.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
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.
- TCM output driver stuck onCommon
- Control wire shorted to a permanent B+ supplyPossible
- Carbon or debris buildup preventing free movementLess likely
Parts involved
- Aux Trans Pump B
- Control Module
- Wiring Harness
P27A6 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.