Powertrain, generic · Hybrid propulsion

P0C20 Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0C20 means at least one of the three motor phases of the auxiliary transmission fluid pump carries no current, typically an open lead, terminal or winding. GM uses it in the pump controller of the Chevrolet Volt (2011-15 tables) and the 2016 Cadillac ELR: with the inverter in Run, high voltage above 35 V and the rotor within 30 degrees of a phase axis, the peak current of that phase is checked; below 1 A for 200 counts sets the code, Type A, MIL on the first trip. Each phase is tested in turn as the rotor turns. The pump cannot build torque, so pressure support and electric operation are lost. Later GM tables split the check into the per-phase codes P0B01, P0B04 and P0B07; P0C21/P0C22 are the low and high variants.

Likely causes

Motor connector of the pump not fully seated, or loose phase terminal
Open phase lead between pump inverter and motor
Power switch of one phase in the pump inverter not conducting
Open winding in the pump motor

Symptoms

  • MIL and Service Vehicle Soon message
  • Reduced propulsion or no electric drive mode
  • Engine restart harsh or delayed

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–2,500
Time0.5–6 h

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

Parts involved

aux trans pump phase uvwaux trans pump inverter

Related codes

P0C21P0C22P0B01P0B04P0B07P0C28

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