P28D2

Code

Generic P — Powertrain

Clutch B Motor Phase U-V-W Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 17 EN: 26 RU: 18

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Damaged or shorted phase wiring (U, V or W) between inverter and motor
Poor or corroded connector or terminal connection at motor, inverter or junction
Short to ground on one or more motor phase conductors
Open or shorted inverter power semiconductor(s) (IGBT/MOSFET) or inverter internal fault
Failed motor winding (open or shorted turns) or internal motor short
Faulty inverter/vehicle control module software or internal electronics

Read stored and pending codes with a compatible scan tool and record freeze-frame/data
Check for additional related codes (inverter, DC bus, current sensors, fuses)
Visually inspect high-voltage harness, connectors, and protective sleeving for damage, corrosion, or water contamination
Verify secure mounting and condition of motor and inverter ground/EMI connections
Measure DC bus voltage and vehicle 12 V battery state while attempting to reproduce the fault
Using insulated tools and HV safety protocols, measure continuity and resistance between motor phases (U-V, V-W, W-U) and phase-to-ground

Expected: When the inverter is commanding torque, phase voltages will switch between approx. 0 V and the DC bus voltage (varies by vehicle — typically tens to several hundred volts). Low/flat phase voltages during drive indicate circuit low condition.
Expected phase-to-phase resistance (motor stator): low value (milliohm to ohm range depending on design); large asymmetry or open indicates winding/inverter issue.
Phase-to-ground/insulation: high resistance (typically >>1 MΩ) on a healthy motor/inverter assembly; low insulation indicates short to ground.
Phase current: should follow commanded torque; a stuck-at-low or zero current on one phase while others show current suggests a phase circuit fault.
DC bus voltage: should be within vehicle spec while inverter is active; low DC bus can cause low phase amplitudes.

Retrieve all codes and live data with a manufacturer-capable scan tool. Note freeze-frame and conditions when fault set.
Inspect wiring and connectors for visible damage, corrosion, water intrusion or loose pins at inverter, motor, and any junctions.
Check fuses, contactors and service interlocks for continuity and correct operation. Replace blown or faulty items.
With high-voltage system disabled and locked out per safety procedures, measure continuity and DC resistance between phases (U-V, V-W, W-U). Compare to spec or to the opposite motor on twin setups.
Measure insulation resistance phase-to-ground using an appropriate HV insulation tester (megger). Do not perform without proper PPE and training.
Re-enable the HV system only when safe. With a qualified technician and appropriate insulated equipment, monitor real-time phase voltages and currents while commanding motor operation. Look for a phase showing low or no voltage/current.
Wiggle-test and load-test connectors and harness while monitoring data to identify intermittent faults.
If wiring/connector checks are good and motor windings and insulation are within spec, suspect inverter/module failure. Confirm with manufacturer diagnostics; replacement or module swap may be required.
After repairs, clear codes, perform functional tests and road-test to verify the fault does not return.

Chafed harness causing intermittent short to ground on a phase conductor
Corroded/loose inverter-to-motor connector pins
Inverter half-bridge or transistor failure causing one phase to sit at low voltage
Open or high-resistance phase connection leading to low measured phase voltage
Motor internal short or grounding fault