P0C55

What it means

P0C55 means the hybrid or electric vehicle control unit has detected a fault in the circuit of the position sensor for drive motor B (the second traction motor or generator, depending on the vehicle). The motor position sensor, usually a resolver or encoder, tells the control unit the rotor angle so it can time the inverter output correctly. The code sets when the signal is missing, out of range, implausible or noisy. The exact sensor type, motor numbering and trigger conditions depend on the model.

Symptoms

• Hybrid or EV system warning light on, often with the main fault lamp
• Reduced power or limp-home mode
• Car refusing to enter Ready mode or shutting down the electric drive while driving
• Engine running more than normal on a hybrid, or poor economy
• Rough or jerky drive-away, or a vibration from the motor
• Intermittent faults that come and go with temperature or vibration

Possible causes

• Damaged, chafed or corroded wiring or connector at the motor position sensor circuitlikely
• Faulty motor position sensor (resolver or encoder) in drive motor Blikely
• Poor terminal contact or water ingress in the motor or inverter connectorpossible
• Fault in the inverter or motor control unit that processes the sensor signalpossible
• Electrical interference or a shorted or open circuit caused by earlier damage, such as a repair or impactpossible
• Mechanical problem with the motor, such as sensor mounting or rotor misalignmentrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting whether other drive motor or inverter codes are present.
2. Check for relevant technical service bulletins and software updates for the specific model and system.
3. Visually inspect the motor position sensor wiring and connectors for chafing, heat damage, corrosion, moisture and loose or pushed-out terminals, without touching any high-voltage components.
4. Only a technician trained in high-voltage systems should continue: isolate the high-voltage system following the manufacturer procedure and confirm it is safe before working near the motor or inverter.
5. Check the sensor circuit for continuity, short to earth, short to supply and resistance between pins against the manufacturer specification.
6. Measure the sensor coil resistance or signal against the specification for that model, as the sensor type varies.
7. View live data for motor B rotor position and speed while the system is operating, looking for dropouts, noise or implausible values.
8. If the wiring and sensor test fine, check the inverter or control unit connections and power and earth supplies before suspecting the unit.

How to fix

• Repair or replace damaged wiring, and clean or replace corroded or damaged connectors and terminals.
• Replace the motor position sensor, or the motor assembly if the sensor is not serviceable separately, and set it up as the manufacturer requires.
• Seal and dry any connector affected by water ingress, and fix the source of the leak.
• Update the control unit software if a known fault exists for this model.
• Repair or replace the inverter or control unit only after the wiring and sensor have been proven good.
• Clear the code after repair and road test to confirm it does not return.

Can I keep driving?

Nearby codes

• P0C54GenericDrive Motor A Position Sensor Circuit A Intermittent/Erratic
• P0C56GenericDrive Motor B Position Sensor Circuit A Range/Performance