P0C66

What it means

P0C66 is a generic powertrain code meaning the control unit has detected a low signal voltage in the generator position sensor circuit A. This sensor reports the rotor position of the generator motor, which is used on hybrid and electric drive systems to time its operation. The code sets when the signal sits below the expected range, which points to a short to ground, an open circuit, a poor connection or a failed sensor. Exact sensor type, wiring and set conditions vary by manufacturer and model.

Symptoms

• Hybrid system or check engine warning light on
• Reduced power or the car going into a limp-home mode
• Engine will not start or stalls, or the hybrid system will not go to ready
• Rough running or poor engine start-up on hybrid models
• Loss of regeneration or poor battery charging
• Noticeably poor fuel economy

Possible causes

• Damaged, chafed or shorted wiring in the generator position sensor circuit (signal shorted to ground or open circuit)likely
• Corroded, loose or water-contaminated connector at the generator or control unitlikely
• Faulty generator position sensor (resolver or equivalent)likely
• Sensor supply or reference voltage fault from the control unitpossible
• Mechanical damage or misalignment affecting the generator rotor and sensorrare
• Faulty hybrid or motor control unitrare

How to diagnose

1. Read all stored codes and freeze frame data, noting whether the fault is current or intermittent and any related generator or motor codes.
2. Check for manufacturer service bulletins and known issues for the specific model and drive system.
3. Visually inspect the generator sensor wiring and connectors for chafing, heat damage, fluid ingress, bent pins and corrosion, taking high-voltage safety precautions around hybrid components.
4. Wiggle test the harness and connectors with live data showing the sensor signal to see if the fault appears or drops out.
5. With the system safely shut down and following the manufacturer's high-voltage isolation procedure, check the circuit for continuity, short to ground and resistance against the specification for that model.
6. Check the sensor supply and reference voltage and the signal against the manufacturer's values.
7. Measure the sensor or resolver coil resistance if the manufacturer gives a specification for it.
8. If wiring and sensor test good, check for control unit faults and software updates as per the manufacturer's procedure.

How to fix

• Repair or replace the damaged wiring section, ensuring correct routing and protection.
• Clean, repair or replace corroded or damaged connectors and terminals, and seal against moisture.
• Replace the generator position sensor, or the generator assembly if the sensor is not serviced separately, then follow any relearn or calibration procedure.
• Correct the supply or reference voltage fault at its source.
• Repair or replace the control unit only after all other causes are ruled out, and apply any software update the manufacturer specifies.

Can I keep driving?

Nearby codes

• P0C65GenericGenerator Position Sensor Circuit A Range/Performance
• P0C67GenericGenerator Position Sensor Circuit A High