The P0666 trouble code indicates a fault with the internal temperature sensor circuit in the Powertrain Control Module (PCM), Engine Control Module (ECM), or Transmission Control Module (TCM). The internal temperature sensor monitors the temperature of the module to ensure it operates within safe limits. When this sensor circuit malfunctions, it can affect the module’s ability to regulate engine or transmission functions properly.
PCM/ECM/TCM Internal Temperature Sensor Circuit
Code symptoms P0666.
1. Check Engine Light (CEL) illuminated on the dashboard.
2. Possible drivability issues, such as rough idle, hesitation, or stalling.
3. Decreased engine or transmission performance.
4. Vehicle may go into a limp mode to prevent further damage.
5. Other related trouble codes may be present.
This code is common in brands such as:: Chevrolet, Renault, Ford, Toyota, Nissan, Mercedes Benz, Honda.
Causes of the code P0666.
1. Faulty internal temperature sensor.
2. Wiring or connector issues in the temperature sensor circuit.
3. Internal fault within the PCM, ECM, or TCM.
Code Solutions P0666.
1. Use a diagnostic scanner to retrieve freeze frame data and all associated trouble codes. This information can help pinpoint the root cause of the issue.
2. Inspect the wiring and connectors related to the internal temperature sensor circuit for any signs of damage, corrosion, or loose connections. Repair or replace damaged components as needed.
3. Test the internal temperature sensor using a digital multimeter to ensure it is within the specified resistance range. Replace the sensor if it is out of range.
4. If the sensor and wiring are in good condition, but the code persists, it may indicate an internal fault within the PCM, ECM, or TCM. In this case, the module may need to be replaced or reprogrammed by a qualified technician.
5. After any repairs are made, clear the trouble codes and perform a test drive to verify that the issue has been resolved. If the code returns, further diagnosis may be necessary to identify the underlying problem.
6. Follow manufacturer-specific diagnostic procedures outlined in the vehicle’s service manual to accurately diagnose and repair issues related to the internal temperature sensor circuit. If needed, seek assistance from a qualified technician or dealership.