P0B00Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL or hybrid/transmission warning message
- Engine auto-stop disabled or no electric drive mode
- Delayed engagement or harsh restart after a stop
- Likely causes
- 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
- RareWinding fault in phase U of the pump motor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.