Powertrain, generic · Hybrid propulsion

P0B08 Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B08 is set when the current in phase W of the auxiliary transmission fluid pump motor rises above the permitted limit. No manufacturer documents this exact code in public sources. In GM's 2016 Volt calibration the equivalent protection is P0C28, which fails on any phase above 35 A or on a d-axis current below a temperature-dependent limit, both within milliseconds to protect the IGBTs. A W-specific high code points to a short in the W lead or winding, a binding pump or a sensing error; the Hitachi patent shows the W value may be calculated rather than measured directly. CARB requires such output drivers to be monitored for circuit faults. The pump shuts down, so start-stop and electric driving are restricted. P0B07 is the low side, P0B02 and P0B05 phases U and V.

Likely causes

Phase W 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 W of the pump motor

Symptoms

  • MIL and transmission or hybrid warning
  • Auxiliary pump shuts down, auto-stop disabled

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 waux trans pump control modulewiring harness

Related codes

P0B02P0B05P0B06P0B07P0C22P0C28

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