P0C08

Code

Generic P — Powertrain

Drive Motor B Phase U-V-W Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 30 EN: 77 RU: 39

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Page language: EN

Causes

Open or broken phase conductor (U, V or W) between inverter and motor
Corroded, loose or disconnected high-voltage phase connector
Internal open in motor winding (broken coil or lead)
Failed inverter power device (IGBT/MOSFET) or output transistor driver
Blown fuse, damaged contactor, or interrupted HV bus feeding inverter
Water ingress or mechanical damage to motor or wiring harness

Symptoms

Immediate drive/traction fault and reduced or no propulsion
Illumination of MIL/EV system warning lights and possible limp-home mode
Loss of torque or one-wheel drive (depending on vehicle)
Unusual motor/noise on attempt to drive or no rotation
Regeneration disabled or reduced
DTC present for drive motor/inverter

What to check

Read stored codes and freeze frame data with a compatible scan tool; record PID values
Verify vehicle in a safe, immobilized state and follow HV safety procedures before any HV inspection
Visually inspect inverter-to-motor phase cables, connectors and boots for damage, contamination or loose pins
Check HV fuses, contactors/relays and DC bus voltage to inverter
Check for separate related codes (inverter, battery, isolation faults)
Measure phase-to-phase and phase-to-ground resistance with proper isolation and procedures

Signal parameters

Expected: symmetrical PWM drive signals from inverter to all three phases (U/V/W) during motor commands
Expected: motor phase-to-phase voltages show alternating AC waveform under drive; when stationary and inverter off, phases may be open/high impedance
Expected: phase currents present and similar magnitudes across phases when under load
Expected: DC bus voltage present and stable feeding inverter
Abnormal: one phase voltage or current near zero while others show normal values indicates open circuit

Diagnostic algorithm

Retrieve and record all related DTCs and freeze-frame data. Note operating conditions when fault set.
Clear codes and attempt to reproduce while monitoring live data for phase voltages/currents, inverter status and HV bus voltage.
Perform thorough visual inspection of inverter-to-motor harness, connectors and motor entry point for damage, corrosion, burned pins or moisture.
With high-voltage system disabled and isolated per manufacturer procedures, measure DC isolation resistance and inspect high-voltage fuses/contactors for continuity.
Measure phase-to-phase and phase-to-ground resistances at the motor connector and at the inverter output (with HV isolated). Compare with vehicle-specific reference; an open/high resistance indicates broken conductor or winding.
If wiring and connectors are good, with appropriate HV safety tools measure phase voltages and currents during a controlled test (using manufacturer-approved procedures and equipment such as an oscilloscope or current probes). Look for missing PWM on one phase.
Swap or substitute suspect components if possible (known-good inverter or motor) or perform bench tests on motor/inverter when authorized and equipped.
Inspect motor windings for continuity and insulation breakdown if accessible; consider motor disassembly only if qualified.
Repair or replace damaged wiring, connectors, motor or inverter as indicated. Reassemble, clear codes and perform functional test drive and live-data verification.
After repair, confirm no related stored faults, and verify regeneration, torque delivery and normal phase balance under load.

Likely causes

Damaged/crimped phase cable or pin (U/V/W) at connector
Open motor winding or broken terminal at motor junction
Inverter output transistor(s) failed open on phase B outputs
Poor pin contact/corrosion inside phase connector
HV interlock/fuse/contact not supplying inverter output stage

Fault status

⚠️ Status

Drive Motor B Phase U-V-W Circuit/Open — one or more motor phase outputs from the inverter are open or disconnected, preventing proper motor operation. Check phase wiring, connectors, motor windings and inverter output stage.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1.0-4.0 hours