P28C6

Code

Generic P — Powertrain

Clutch A Motor Phase U-V-W Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 16 EN: 30 RU: 23

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Page language: EN

Causes

Broken or disconnected phase conductor (U, V or W) between inverter/drive and motor/clutch
Poor or corroded connector/terminal (pin pushed out, bent, or oxidized)
Internal motor winding open or damaged stator winding
Failed inverter/power module output stage (power transistor/IGBT open)
Blown fuse, tripped contactor, or failed relay in the motor power feed
High-resistance joint or poor crimp causing intermittent open under load

Symptoms

Clutch A motor will not run or clutch will not engage
Drive system enters limp or fault mode with reduced functionality
Malfunction Indicator Lamp (MIL) or system warning light illuminated
Unusual clicking, no motor response, or inconsistent torque from clutch
Stored DTC(s) corresponding to phase circuit/open

What to check

Read freeze-frame and full DTC list from the vehicle controller; note related codes
Perform a careful visual inspection of phase wiring, harness, and connectors for damage, corrosion, or loose pins
Verify fuses, circuit breakers and contactors in the motor power feed are intact and operating
Check for signs of overheating or water ingress at motor or inverter
Confirm software/calibration is current if a known software fix exists for related failures

Signal parameters

Phase-to-phase continuity: very low resistance (typically milliohms to low ohms depending on motor design) — open/infinite if circuit open
Phase-to-ground insulation: very high resistance (megaohms expected) — low values indicate short to ground
DC bus voltage present at inverter inputs when motor is commanded (battery pack voltage range for vehicle)
Phase voltage waveforms under command: PWM/AC waveform on all three phases when motor is driven; missing phase indicates open
Stator current: expected balanced three-phase currents during operation; zero or missing phase current if open

Diagnostic algorithm

Retrieve and record all related DTCs and freeze frame data; clear codes and attempt to re-create the fault under controlled conditions to confirm persistence.
Visually inspect connectors and harness from the controller/inverter to the Clutch A motor — look for disconnected pins, corrosion, chafing, or rodent damage.
With ignition off and high-voltage safety procedures followed, disconnect motor connector and check continuity between inverter outputs and motor phase leads (U, V, W). Expect continuity; an open indicates wiring/connector fault.
Measure phase-to-phase resistance of the motor windings (with motor isolated). Compare U-V, V-W, W-U; near-equal low resistances indicate healthy windings. Infinite/open suggests internal motor winding break.
Measure phase-to-ground insulation resistance to verify no short to chassis. Low resistance indicates damage/short to ground.
Inspect/verify fuses, contactors and relays in the motor power feed and replace or test as necessary.
Reconnect and use a scope or diagnostic tool to command the motor while monitoring inverter phase outputs. Check for proper PWM/AC on all three phases. Missing waveform on one phase points to inverter output failure or open conductor.
If inverter outputs are present but motor shows open, suspect internal motor wiring/winding failure and consider motor replacement or internal repair.
If wiring and motor check good but no phase output from inverter, diagnose inverter/power module (check gate drivers, power devices) or replace module per manufacturer procedure.
After repair, clear codes and perform operational test under load to confirm the fault is resolved. Monitor for intermittent faults.