P0B0A code meaning
Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit Low
Powertrain system Generic code P0Bxx codes Check engine light
What P0B0A means
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.
P0B0A at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0B0A
- Start-stop function inactive
- MIL or transmission warning
- Jerky drive-off after an engine stop
Common causes of P0B0A
- Most likelyCorroded terminal or high resistance in the pump feed or ground
- PossibleWeak 12 V battery or poor charging
- Less likelyDC/DC converter or alternator output too low (hybrid)
- Less likelyVoltage sensing input in the controller faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aux trans pump a motorWiring harnessTCM
What each part of P0B0A means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B | Area: hybrid propulsion. |
| 0A | The exact fault in that area. |
What to do next
- Note P0B0A 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 P0B0A
What does P0B0A mean?
P0B0A means "Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit Low". P0B0A means the supply voltage measured at the motor of auxiliary pump A is lower than expected while the pump should be running. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B0A?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0B0A fail an emissions test?
Yes, it can. P0B0A is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0B0A to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0B0A 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.