Powertrain, generic · Hybrid propulsion

P0B00 Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Loose, corroded or unlatched phase U connection at the pump motor
Current sensing in the pump inverter faulty (shunt or phase sensor)
Power stage of phase U in the pump control module faulty
Winding fault in phase U of the pump motor

Symptoms

  • MIL or hybrid/transmission warning message
  • Engine auto-stop disabled or no electric drive mode
  • Delayed engagement or harsh restart after a stop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,500
Time1–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

aux trans pump motor phase uaux trans pump control modulewiring harness

Related codes

P0B01P0B02P0B03P0B06P0C20P0C28

References: law.cornell.edu, patents.google.com, gsi.ext.gm.com.