01 Drivers Are Accidentally Destroying Their Cars By Trusting … • 02 This Is Why Your Car’s Headlights Are Dim • 03 Decoding the Engine Control Unit (ECU): Inputs, Outputs, an… • 04 12 Luxury Cars Owned by Footballers That Cost More Than a P… • 05 P0101 - Mass Air Flow (MAF) Sensor Performance • 06 Engine Oil Sludge: The Silent Threat to Your Vehicle's Perf… • 07 Stellantis: The Birth of a New Automotive Star from FCA and… • 08 Prevent Disaster: The Ultimate Guide to Installing Cotter (… • 09 Toyota Warning Light Symbols and Meanings: A Comprehensive … • 10 Troubleshooting Car Battery Drain: A Comprehensive Guide •

DTC codes / P0Cxx · Hybrid propulsion / P0C22

P0C22Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit High

P0C22 indicates that the transmission control module (TCM) has detected a high-voltage condition on the electrical circuit for phase U, V, or W of the auxiliary transmission fluid pump. This pump, often electric, maintains fluid pressure for functions like stop-start or hybrid operation, and the high voltage suggests a short to power, an open circuit, or a faulty pump motor winding.

SystemPowertrain
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard.
  • Transmission may enter limp mode or fail to engage drive or reverse.
  • Harsh or delayed shifting, or inability to shift gears.
  • Overheating of the transmission due to inadequate fluid circulation.
  • Often no symptoms besides the warning light, especially if the pump is only used under specific conditions.

Common causes, most likely first

  1. Damaged or shorted wiring in the pump phase circuit (U, V, or W) contacting a power source.
  2. Faulty auxiliary transmission fluid pump motor with internal winding short.
  3. Corroded, loose, or disconnected electrical connectors at the pump or TCM.
  4. Failed transmission control module (TCM) driver circuit for the pump.
  5. Poor ground connection for the pump or TCM, causing voltage spikes.
  6. Aftermarket accessories or improper wiring repairs interfering with the circuit.

How to diagnose and fix it

  1. Perform a visual inspection of the pump wiring harness and connectors for chafing, corrosion, or loose pins.
  2. Use a digital multimeter to check for battery voltage on the phase circuits with the pump commanded off; any voltage indicates a short to power.
  3. Measure resistance across the pump motor phases (U-V, V-W, W-U) and compare to specifications; an open or short indicates a faulty pump.
  4. Check the pump ground circuit for excessive resistance and repair as needed.
  5. Inspect the TCM connectors for signs of damage or water intrusion and verify TCM software is up to date.
  6. If wiring and connectors are good, substitute a known-good pump or TCM to isolate the fault.
  7. Clear the code and perform a road test to verify the repair, ensuring the pump activates under the conditions that originally set the code.

Before condemning the auxiliary pump

  • A high voltage code on a pump phase circuit is often caused by a short to power in the harness, not by the pump itself, so always check for voltage on the phase wires with the pump disconnected.
  • The auxiliary pump may only run during auto start-stop events or when the engine is off in a hybrid, so the code may not set during a normal test drive; use a scan tool to command the pump on.
  • Corrosion inside the pump connector can create a high-resistance path that mimics a phase fault, so inspect the terminals closely even if they look clean from the outside.
  • A failing TCM power supply or ground can cause erratic pump operation and set this code without any fault in the pump circuit, so verify powers and grounds at the TCM first.
  • This code can be stored alongside other phase codes (P0C23, P0C24) if multiple phases are affected, often pointing to a shared connector or harness issue rather than multiple pump failures.

Can I keep driving with P0C22?

If the vehicle drives normally, you may cautiously drive to a repair shop, but avoid heavy loads or long distances because the transmission may overheat if the pump is not working. If the transmission is in limp mode or slipping, stop driving and have the vehicle towed to prevent further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage