P0B09Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P0B09 concerns the power feed of auxiliary pump A's motor: the controller sees no valid supply voltage, usually because the circuit is open. GM documents it for its 2012-13 eAssist mild hybrids (BAS Plus): the hardware input reports an out-of-range voltage flag on the auxiliary pump circuit, enabled with ignition voltage above 9 V; failing for at least 0.375 s within a 1.2 s sample sets P0B09 as Type B, MIL after two trips. A related GM check, P2797, verifies during auto-stops that the pump draws power and that turbine speed does not flare on restart. A Hitachi patent on a battery-fed sub-oil pump shows the controller inhibits engine auto-stop when pump current behaves abnormally. Typical results: no auto-stop and a lamp. P0B0A/P0B0B are the low and high variants.
- What you may notice
- Engine auto-stop no longer occurs
- MIL after two drive cycles
- Shift flare or delayed drive engagement on restart
- Likely causes
- LikelyBlown fuse or open relay in the pump supply
- LikelyOpen supply wire or loose terminal at the pump connector
- PossiblePoor ground connection of the pump motor
- RareVoltage sensing input in the controller faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.