Powertrain, generic · Hybrid propulsion

P0B02 Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B02 reports excessive current in phase U of the auxiliary transmission fluid pump motor, an overcurrent condition that the pump inverter must cut off to protect its switches. No manufacturer documents this exact code publicly. GM handles the same case differently: on the Volt and later hybrids it sets P0C28 when the absolute current of any phase exceeds 35 A for a few milliseconds, Type A. A phase-specific high code therefore points to a shorted U lead, a shorted winding, a jammed pump or a U current sensor reading too high. The Hitachi idle-stop pump patent shows phase currents being reconstructed from one bus shunt, which makes a sensing error a real candidate. The pump usually stops; auto-stop or electric driving is blocked. P0B01 is the low side, P0B05 and P0B08 the same fault on V and W.

Likely causes

Phase U lead shorted to another phase or to ground
Pump binding mechanically, raising motor current
Current sensing in the pump inverter reads too high
Shorted turns in phase U of the pump motor

Symptoms

  • MIL and transmission or hybrid warning
  • Auxiliary pump shuts down, auto-stop disabled
  • Harsh or delayed engagement after an engine stop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€200–2,500
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

P0B00P0B01P0B05P0B08P0C22P0C28

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