Powertrain, generic · Hybrid propulsion

P0C09 Drive Motor B Phase U-V-W Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0C09 marks a U, V or W phase line of drive motor B that is pulled low, for example by a short to the negative high-voltage rail, to ground or by a power switch that conducts when it should not. It is the motor B twin of P0C06; the siblings P0C08 and P0C0A cover an open phase and a phase stuck high. No manufacturer documents P0C09 publicly, and GM's hybrid tables use only P0C08 for motor B phase circuits. CARB requires circuit fault monitoring of hybrid components. A low phase usually causes overcurrent too, so P0C04 or insulation codes often accompany it. The motor controller switches motor B off; the vehicle continues with reduced power and a warning lamp.

Likely causes

Phase cable or winding of motor B shorted to ground or housing
Shorted low-side power switch in the motor B inverter
Insulation damage from heat, moisture or chafing

Symptoms

  • Motor B shut down with warning lamp
  • Overcurrent or insulation codes stored at the same time

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€200–6,000
Time1–10 h

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

Parts involved

drive motor b phase uvwdrive motor b inverter

Related codes

P0C08P0C0AP0C06P0C04P0BFE

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