P0B09 code meaning
Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit/Open
Powertrain system Generic code P0Bxx codes Check engine light
What P0B09 means
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.
P0B09 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 P0B09
- Engine auto-stop no longer occurs
- MIL after two drive cycles
- Shift flare or delayed drive engagement on restart
Common causes of P0B09
- Most likelyBlown fuse or open relay in the pump supply
- Most likelyOpen supply wire or loose terminal at the pump connector
- PossiblePoor ground connection of the pump motor
- 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 P0B09 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. |
| 09 | The exact fault in that area. |
What to do next
- Note P0B09 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 P0B09
What does P0B09 mean?
P0B09 means "Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit/Open". P0B09 concerns the power feed of auxiliary pump A's motor: the controller sees no valid supply voltage, usually because the circuit is open. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B09?
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 P0B09 fail an emissions test?
Yes, it can. P0B09 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 P0B09 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 P0B09 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.