The P0668: PCM/ECM/TCM Internal Temperature Sensor Circuit Low code indicates that the control module (PCM/ECM/TCM) has detected low voltage in the internal temperature sensor circuit. This sensor monitors the temperature of the module to ensure proper function and prevent overheating. Low voltage could result from a faulty sensor, wiring issues, or problems within the control module itself.
P0668 – Quick Overview
| Code | Information |
|---|---|
| Meaning | P0668: PCM/ECM/TCM Internal Temperature Sensor Circuit Low |
| Is it serious? | Yes, as it can lead to overheating and improper function of the control module. |
| Possible causes | – Low voltage in internal temperature sensor circuit in PCM/ECM/TCM – Faulty sensor – Wiring issue |
| How to diagnose? | – Test internal temperature sensor circuit for voltage – Inspect wiring and connectors – Replace PCM/ECM/TCM if necessary |
P0668 Meaning
The P0668 code indicates that the control module (PCM, ECM, or TCM) has detected lower-than-expected voltage in its internal temperature sensor circuit. This sensor helps monitor the internal temperature of the module to avoid overheating. A low voltage condition can affect the accuracy of temperature readings, leading to incorrect thermal management and potentially causing module failure.
Step-by-step diagnostic guide
| Action | Description | Tools Needed |
|---|---|---|
| Check for Other Codes | Use an OBD-II scanner to check for additional related codes that might provide further context, especially those related to the control module’s performance. | OBD-II Scanner |
| Test the Internal Temperature Sensor Circuit for Voltage | Use a multimeter to measure the voltage in the internal temperature sensor circuit. Verify that the voltage is within the manufacturer’s specified range. | Multimeter |
| Inspect Wiring and Connectors | Inspect the wiring and connectors leading to the PCM/ECM/TCM for signs of damage, loose connections, or corrosion that could be causing a low voltage condition. | Flashlight, Multimeter |
| Test the Internal Temperature Sensor | Test the internal temperature sensor within the control module to ensure it is functioning properly and providing accurate temperature readings. Replace if necessary. | Diagnostic Tool, Multimeter |
| Replace the PCM/ECM/TCM if Necessary | If the sensor or circuit within the PCM/ECM/TCM is determined to be faulty, replace the control module to restore proper temperature monitoring. | 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 module are functioning correctly. | OBD-II Scanner, Vehicle Manual |
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