Powertrain, generic · Hybrid propulsion

P0C08 Drive Motor B Phase U-V-W Circuit/Open

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P0C08 is the open-phase check for drive motor B, the motor B twin of P0C05. GM runs it on the 2011 Volt and the 2012 two-mode trucks: each phase is checked as the rotor passes its axis, and a phase axis current below 9 A while at least 23 A is commanded, with the rotor within 30 degrees and over 35 V on the inverter, counts as a miss. Around 200 failed samples set it, Type A, one trip. Later GM tables up to 2016 keep the same logic. GM's eAssist has only one machine and no P0C08. The usual causes are a loose three-phase terminal, an open stator winding or an inverter stage that does not conduct. Motor B then delivers no torque, the MIL lights and drive power is reduced.

Likely causes

Loose or open three-phase terminal between inverter and motor B

Open stator winding in drive motor B

Inverter stage for motor B not conducting

Symptoms

Malfunction indicator lamp after one drive
Reduced propulsion power
Engine running more often than usual

Repair estimate

DifficultyShop_onlyWorkshop job

Parts and labour€100–5,000

Time0.5–8 h

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

Parts involved

drive motor b phase uvwdrive motor b inverter

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.