P0C20 code meaning
Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open
Powertrain system Generic code P0Cxx codes Check engine light
What P0C20 means
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.
P0C20 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0C20
- MIL and Service Vehicle Soon message
- Reduced propulsion or no electric drive mode
- Engine restart harsh or delayed
Common causes of P0C20
- Most 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
- Less likelyOpen winding in the pump motor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aux trans pump phase uvwAux trans pump inverter
What each part of P0C20 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| C | Area: hybrid propulsion. |
| 20 | The exact fault in that area. |
What to do next
- Note P0C20 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0C20
What does P0C20 mean?
P0C20 means "Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0C20?
Drive gently and only to a workshop. With P0C20 the car can go into limp mode (reduced power) to protect itself.
Will P0C20 fail an emissions test?
Yes, it can. P0C20 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0C20 to fix?
Difficulty: hard. A typical repair takes 0.5 to 6 hours of work. This is a job for a workshop.
Will P0C20 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.