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DTC codes / P0Cxx · Hybrid propulsion / P0C0A

P0C0ADrive Motor B Phase U-V-W Circuit High

P0C0A indicates that the inverter or motor control module has detected an abnormally high voltage or current on the U, V, or W phase circuit of drive motor B, which is the second electric motor in a hybrid or electric vehicle's propulsion system. The computer compares commanded phase outputs against actual feedback and flags this code when the circuit exceeds safe limits, often due to a short to voltage, a failing motor winding, or a damaged cable.

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

Symptoms you may notice

  • Illumination of the check engine light or hybrid/EV system warning lamp
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Reduced power or limp-home mode with limited motor B operation
  • Rough running or shuddering during electric-only propulsion
  • Overheating of the inverter or motor, leading to power derating
  • In rare cases, a sudden loss of propulsion or failure to start

Common causes, most likely first

  1. Damaged or chafed phase cable between the inverter and motor B, causing a short to voltage or ground
  2. Failed motor B stator winding with insulation breakdown or shorted turns
  3. Faulty inverter assembly with internal shorted power transistors or driver circuit failure
  4. Loose or corroded high-voltage connector pins at the motor or inverter
  5. Coolant contamination or overheating of the inverter leading to component stress
  6. Software calibration error in the motor control module (rare, often requires reflash)

How to diagnose and fix it

  1. Perform a visual inspection of the high-voltage phase cables and connectors for chafing, corrosion, or loose pins
  2. Use a scan tool to read live data and freeze-frame information for motor B phase voltage and current
  3. Measure insulation resistance and continuity of the U, V, and W phase cables with a megohmmeter, following manufacturer safety procedures
  4. Check motor B winding resistance and insulation to ground using a low-resistance ohmmeter and megohmmeter
  5. Inspect inverter cooling system for leaks or blockages that could cause overheating
  6. If cables and motor test good, substitute a known-good inverter or motor control module for diagnosis
  7. After repair, clear codes and perform a road test to verify the fault does not return

High-voltage phase faults often misdiagnosed

  • A chafed phase cable rubbing against a metal bracket is a common cause that many technicians overlook when they focus on the motor or inverter.
  • The code can be set by a loose high-voltage connector pin that only loses contact during vibration, so a static inspection may not reveal the problem.
  • Motor B phase faults sometimes appear after a coolant leak contaminates the inverter, so always check for dried coolant residue around connectors.
  • Replacing the inverter without first testing the phase cables and motor windings can lead to a repeat failure if the root cause is external.
  • Some vehicles set P0C0A as a companion code to other hybrid system faults, so diagnosing the primary code first may resolve this one.

Can I keep driving with P0C0A?

Do not continue driving with this code active, because a high-voltage phase fault can cause sudden loss of propulsion or further damage to the inverter and motor. Have the vehicle towed to a qualified hybrid/EV service facility for diagnosis.

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.

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