What it means
The drive motor B phase U-V-W output reports a circuit low condition. The drive motor's position, current and temperature are watched continuously; a fault here downgrades the inverter to a safe operating point or triggers torque reduction.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The inverter supplies Drive Motor B through its U, V, and W phase outputs, using switching devices to control motor current. P0C09 sets when the module detects a phase output that is too low, which can point to a phase wire shorted to ground, a failed low-side inverter switch, or corroded pins with high contact resistance.
Common causes
Most likely first.
- Phase wire shorted to ground
- Low-side switch open in inverter
- Connector pins corroded - high contact resistance
Symptoms
- EV/hybrid system warning light on
- Reduced motor power or torque
- Possible limp mode or vehicle shutdown
How to diagnose it
- Review freeze-frame and live data for Drive Motor B phase output, current, requested torque, and related inverter faults to determine when the low condition appears.
- With the high-voltage system disabled under the manufacturer's procedure, inspect Drive Motor B's U, V, and W wiring for damaged insulation or contact with ground.
- Inspect the phase connector pins for corrosion, looseness, or heat damage that could raise contact resistance.
- Have a qualified technician test the Drive Motor B phase wiring for a short to ground using the manufacturer's isolation procedure.
- If the harness and terminals are sound, test the inverter low-side switching output against the manufacturer's specification.
Common fixes
- Clean or repair corroded Drive Motor B phase terminals.
- Repair wiring that is shorted to ground or has damaged insulation.
- Replace a connector or pin that cannot maintain a sound phase connection.
- Repair or replace the inverter if a low-side switch failure is confirmed.
Can I keep driving?
Drive gently and avoid high power demand because Drive Motor B may lose torque, trigger limp mode, or cause a shutdown. Stop safely if propulsion drops sharply or the hybrid-system warning escalates.
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.