P0B0AElectric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit Low
- 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
- P0B0A means the supply voltage measured at the motor of auxiliary pump A is lower than expected while the pump should be running. No manufacturer documents this exact code publicly; GM's eAssist tables only cover the open-circuit case as P0B09. A Mikuni patent shows why the controller measures this voltage at all: it combines motor current, supply voltage and speed to judge the hydraulic load, so a sagging supply also falsifies pump diagnosis. Causes are high resistance in the feed or ground, a weak 12 V battery, a failing DC/DC converter or a voltage drop when the pump starts. CARB requires circuit checks on such outputs. The pump runs slowly or not at all and start-stop is usually inhibited. P0B09 covers an open circuit, P0B0B a supply that is too high, P0562 low system voltage in general.
- What you may notice
- Start-stop function inactive
- MIL or transmission warning
- Jerky drive-off after an engine stop
- Likely causes
- LikelyCorroded terminal or high resistance in the pump feed or ground
- PossibleWeak 12 V battery or poor charging
- RareDC/DC converter or alternator output too low (hybrid)
- 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 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.