P0B00 code meaning
Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current
Powertrain system Generic code P0Bxx codes Check engine light
What P0B00 means
P0B00 is the general fault for phase U of the three-phase motor that drives the electric auxiliary transmission fluid pump, the pump that keeps line pressure while the engine is stopped. No manufacturer documents this exact code publicly. GM, which runs such pumps on the Volt, ELR, Spark EV and CT6, monitors phase U instead with the low-side code P0B01 and catches overcurrent on any phase with P0C28. A Hitachi patent for an idle-stop sub-oil pump shows that the inverter often derives every phase current from one DC-bus shunt, so a U fault may come from the shared sensor rather than the phase itself. Expect a warning lamp, a stopped pump and, depending on design, no engine auto-stop or a no-start. P0B01/P0B02 are the low and high variants, P0B03 and P0B06 phases V and W.
P0B00 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B00
- MIL or hybrid/transmission warning message
- Engine auto-stop disabled or no electric drive mode
- Delayed engagement or harsh restart after a stop
Common causes of P0B00
- Most likelyLoose, corroded or unlatched phase U connection at the pump motor
- PossibleCurrent sensing in the pump inverter faulty (shunt or phase sensor)
- PossiblePower stage of phase U in the pump control module faulty
- Less likelyWinding fault in phase U of the pump motor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aux trans pump motor phase uAux trans pump control moduleWiring harness
What each part of P0B00 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. |
| 00 | The exact fault in that area. |
What to do next
- Note P0B00 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 P0B00
What does P0B00 mean?
P0B00 means "Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current". P0B00 is the general fault for phase U of the three-phase motor that drives the electric auxiliary transmission fluid pump, the pump that keeps line pressure while the engine is stopped. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B00?
Drive gently and only to a workshop. With P0B00 the car can go into limp mode (reduced power) to protect itself.
Will P0B00 fail an emissions test?
Yes, it can. P0B00 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 P0B00 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will P0B00 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.