Code
P0C06
Generic
P — Powertrain
Drive Motor A Phase U-V-W Circuit Low
Views:
UK: 22
EN: 40
RU: 33
AI status
Completed
Completed
100%
Causes
- Open, short, or high-resistance connection in one or more phase wires (U, V or W)
- Damaged or shorted motor windings (stator) in Drive Motor A
- Failed inverter power module (IGBTs, MOSFETs) or driver circuitry
- Low or missing HV DC bus voltage to inverter (battery/contactor/fuse/connector)
- Poor or corroded high-voltage connectors/terminals
- Blown HV fuse / tripped contactor or relay
Symptoms
- Reduced or no drive torque from affected motor
- MIL (malfunction indicator) / EV warning lamp illuminated
- Vehicle may go into limp or reduced-power mode
- Unusual motor noise, vibration, or single-phase operation
- Hybrid/EV system not ready or unable to accelerate
- Stored freeze-frame data showing low phase voltage/current during fault
What to check
- Safety first: follow manufacturer HV lockout/isolation procedures before any high-voltage work; use PPE and rated tools.
- Retrieve DTCs and freeze-frame data with a capable scan tool; note environmental and operating conditions.
- Visually inspect phase cables, high-voltage connectors, and inverter/motor terminals for damage, corrosion, or signs of overheating.
- Verify HV battery/DC bus voltage is present and within specification with the system in the required state.
- Check HV fuses, contactors/relays and their control circuits for proper operation.
- Measure insulation/continuity of U, V and W phase conductors (with HV system de-energized) and check resistance between phases and to ground.
Signal parameters
- HV DC bus (inverter input) should be at battery pack voltage when system is on (varies by vehicle, typically 200–800 V depending on model).
- During inverter output, phase-to-phase voltages will be PWM-modulated and can vary between ~0 V and near the DC bus voltage; phase-to-phase peak should approximate DC bus voltage.
- When the inverter is commanded to produce torque, measurable phase currents should flow; a complete low condition may show very low or zero phase current in one or more legs.
- Switching/PWM frequency typically in the kHz range — look for absent or abnormal PWM on a failed leg.
- Phase-to-ground voltages should not show low-impedance shorts to chassis ground; insulation resistance should be high (Megohm range).
Diagnostic algorithm
- Read and record all codes, freeze frame data and live PID values related to inverter, motor, DC bus and HV system.
- Check battery pack HV voltage and state; confirm DC link voltage at inverter input is present and stable when commanded.
- Inspect all high-voltage phase cables, connector pins and shielding for damage, corrosion, loose clamps or overheating discoloration.
- With HV system de-energized and isolated, perform continuity and resistance checks: compare U‑V‑W phase-to-phase resistances and phase‑to‑phase symmetry; check phase-to-chassis insulation resistance using a megohmmeter per manufacturer limits.
- Inspect HV fuses and contactors; replace or test as required.
- Re-energize system (follow safety) and use a HV-capable oscilloscope or manufacturer diagnostic tool to monitor phase voltages and PWM signals while commanding a low-speed motor torque / diagnostic run. Look for missing PWM or one leg not switching.
- If one leg of the inverter is not switching but DC bus is present and gate-driver commands are present, suspect inverter power stage failure. Check gate-drive voltages and control signals at inverter connector.
- If inverter outputs are OK but motor phase shows open or abnormal resistance/insulation, suspect motor internal winding damage or short between phases.
- If possible, swap with a known-good inverter or motor (manufacturer-approved procedures) to isolate inverter vs motor fault.
- After repair, clear codes, perform relearns/calibrations as required by manufacturer, and re-test drive cycle to confirm fault does not return.
Likely causes
- Damaged or disconnected phase wiring / high-resistance connector between inverter and motor
- Faulty inverter power stage (one or more failed transistor legs)
- Low HV DC bus (battery disconnected or DC link fault)
- Shorted or open motor phase winding
Fault status
Status
Drive Motor A Phase U‑V‑W Circuit Low — one or more motor phase voltages/currents below expected; check inverter, HV bus, phase wiring and motor.
Repair difficulty: Hard
Diagnostic time: 2.0-6.0 hours
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