The P0666: PCM/ECM/TCM Internal Temperature Sensor Circuit code refers to an issue with the internal temperature sensor circuit of the Powertrain Control Module (PCM), Engine Control Module (ECM), or Transmission Control Module (TCM). This could be caused by a faulty internal temperature sensor, wiring issues, or a malfunction in the PCM/ECM/TCM. This sensor monitors the temperature of the control modules to ensure proper operation and prevent overheating.
P0666 – Quick Overview
| Code | Information |
|---|---|
| Meaning | P0666: PCM/ECM/TCM Internal Temperature Sensor Circuit |
| Is it serious? | Yes, it can lead to incorrect temperature readings, possibly causing improper operation of the control module and system overheating. |
| Possible causes | – Faulty internal temperature sensor circuit in PCM/ECM/TCM – Wiring issue – Faulty PCM/ECM/TCM |
| How to diagnose? | – Test internal temperature sensor circuit – Inspect wiring and connectors – Replace PCM/ECM/TCM if necessary |
P0666 Meaning
The P0666 code indicates that the internal temperature sensor circuit in the PCM, ECM, or TCM is not functioning correctly. This sensor monitors the module’s temperature, and if it fails, the module may overheat or operate inefficiently, affecting engine or transmission performance.
Step-by-step diagnostic guide
| Action | Description | Tools Needed |
|---|---|---|
| Check for Other Codes | Use an OBD-II scanner to check for additional codes related to the PCM, ECM, or TCM that may help further diagnose the internal temperature sensor circuit issue. | OBD-II Scanner |
| Test the Internal Temperature Sensor Circuit | Use a multimeter to test the voltage and continuity of the internal temperature sensor circuit to ensure it is functioning correctly. | Multimeter |
| Inspect Wiring and Connectors | Inspect the wiring and connectors leading to the PCM, ECM, or TCM for signs of damage, loose connections, or corrosion that may affect the internal temperature sensor circuit. | Flashlight, Multimeter |
| Test the PCM/ECM/TCM Internal Temperature Sensor | If accessible, test the internal temperature sensor directly within the control module to verify its operation. If it is not providing accurate readings, replacement may be required. | Diagnostic Tool, Multimeter |
| Replace the PCM/ECM/TCM if Necessary | If the internal temperature sensor or circuit in the PCM/ECM/TCM is faulty and cannot be repaired, replace the module to prevent overheating and system failures. | Replacement PCM/ECM/TCM, Tools |
| Clear the Code and Test | After repairs, clear the code using an OBD-II scanner and test the vehicle to ensure the internal temperature sensor and control modules are functioning properly. | OBD-II Scanner, Vehicle Manual |
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