Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open
The P0C20 code indicates an open or malfunction in the phase U-V-W circuit of the auxiliary transmission fluid pump. This pump is typically found in hybrid or electric vehicles to circulate transmission fluid when the main engine is off. An open circuit means there is a break in the electrical path, preventing the pump from operating correctly. This can lead to inadequate transmission fluid circulation, potentially causing overheating or damage to the transmission.
01. Most Common Causes
- Open or shorted wiring in the pump motor circuit
- Faulty auxiliary transmission fluid pump motor
- Damaged connector or poor electrical connection
- Failed pump control module or relay
02. Symptoms You Will Notice
- Transmission overheating
- Reduced fuel economy in hybrid mode
- Check Engine Light illuminated
- Transmission slipping or harsh shifting
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the pump wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the pump motor resistance and voltage supply using a multimeter.
Step 4: If wiring is intact, replace the auxiliary transmission fluid pump.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a faulty auxiliary pump can cause transmission overheating and potential damage, especially in hybrid vehicles that rely on it for cooling when the engine is off.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnostic and minor repairs like wiring fixes. Pump replacement can be higher, often $200-$500 including parts and labor.