P0C20Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL and Service Vehicle Soon message
- Reduced propulsion or no electric drive mode
- Engine restart harsh or delayed
- Likely causes
- LikelyMotor connector of the pump not fully seated, or loose phase terminal
- PossibleOpen phase lead between pump inverter and motor
- PossiblePower switch of one phase in the pump inverter not conducting
- RareOpen winding in the pump motor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.