What it means
The control module detected a fault associated with drive motor B phase U current. The code alone does not identify whether the cause is in the current measurement circuit, inverter, or motor.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Drive motor B uses phase U as one of its three current paths, controlled by the inverter to produce torque. The module monitors phase U current and sets this code when it detects a fault associated with that measurement; the code alone does not distinguish a sensor, wiring, inverter, or motor problem.
Common causes
Most likely first.
- Phase current sensor failed
- Wiring fault
Symptoms
- EV/hybrid system warning light on
- Reduced motor power or torque
- Possible limp mode or vehicle shutdown
How to diagnose it
- Save freeze-frame data and compare live motor B phase U current with phases V and W while noting the operating condition that triggered the fault.
- Check for companion motor B, inverter, or current-sensor codes that may narrow the fault to the measurement circuit or power stage.
- With the vehicle safely powered down according to the manufacturer’s procedure, inspect the motor B phase U wiring and connectors for corrosion, loose pins, heat damage, or chafing.
- Test the phase U current-sensor supply, ground, and signal circuit for continuity and shorts using the manufacturer’s wiring information.
- If wiring checks pass, test the motor B phase U current sensor and compare the signal with the manufacturer’s specification; then assess the inverter or motor if the sensor is sound.
Common fixes
- Clean and secure a loose or corroded motor B phase U connector.
- Repair damaged phase U wiring or its sensor signal circuit.
- Replace the phase U current sensor if its output fails the specified test.
- Repair the inverter or motor only if follow-up testing isolates the fault to that component.
Can I keep driving?
Limit driving and avoid high loads if motor power is reduced; stop in a safe place if limp mode or a shutdown warning appears. A faulty phase U measurement can cause the hybrid system to limit or lose propulsion, so arrange prompt diagnosis.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.