Powertrain, generic · Hybrid propulsion

P0B03 Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B03 covers a general current fault in phase V of the brushless motor of the electric auxiliary transmission fluid pump. No manufacturer publicly describes a monitor for it. GM's 2013 eAssist (BAS Plus) tables name P0B03 only once, as a code that must be inactive before another speed check runs, without a description of its own. In GM's Volt and CT6 tables phase V is watched by the low-side code P0B04, and any overcurrent goes to P0C28. A GM, BMW and Daimler patent on a hybrid transmission pump explains why the pump matters: it must hold transmission pressure when the engine is stopped, otherwise gear engagement can be lost. The general code is a catch-all for implausible V current that fits neither low nor high. P0B04/P0B05 are the low and high variants, P0B00 and P0B06 phases U and W.

Likely causes

Poor contact in the phase V lead or pump connector
Current sensing in the pump inverter faulty
Phase V power stage in the pump control module faulty
Winding fault in phase V of the pump motor

Symptoms

  • MIL or transmission/hybrid warning
  • Engine auto-stop or electric mode no longer available

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 vaux trans pump control modulewiring harness

Related codes

P0B00P0B04P0B05P0B06P0C20P0C28

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