What Does P0668 Mean?
The PCM/ECM/TCM internal temperature sensor circuit is reading below the minimum expected voltage, indicating a low signal. This typically means the sensor is reporting an excessively high temperature inside the control module (thermistors have inverse voltage-temperature relationships) or there is a short to ground in the internal circuit. The module may enter a protective mode to prevent thermal damage. The driver may notice reduced performance or limp mode activation.
Common Causes
35%
PCM/ECM/TCM actually overheating due to environmental factors
30%
Internal sensor failure within the control module (reading low)
20%
Poor power or ground connections causing voltage reference issues
10%
Control module mounted in excessively hot location or missing heat shield
5%
Water damage or corrosion on PCM circuit board
Diagnostic Steps
1
Immediately check the PCM internal temperature PID — if it reads above 200°F, the module may genuinely be overheating and needs to cool down before further diagnosis.
2
Use an infrared thermometer to measure the actual PCM housing surface temperature and compare to the scan tool internal temp PID. If the PID reads much hotter than the housing surface, the internal sensor is faulty.
3
Inspect the PCM mounting location for adequate airflow and clearance from exhaust components. Verify all OEM heat shields and ducting are intact.
4
Check all PCM power and ground pins for corrosion and proper voltage. Measure voltage drop on each ground circuit (should be less than 0.1V). Clean and tighten as needed.
5
If the module has been exposed to water (flood damage, windshield leak, etc.), inspect for water marks on the connector pins and consider replacement.
Estimated Repair Cost
$200 - $1,600
Parts + labor, varies by vehicle and location
The PCM/ECM/TCM internal temperature sensor circuit is reading below the minimum expected voltage, indicating a low signal. This typically means the sensor is reporting an excessively high temperature inside the control module (thermistors have inverse voltage-temperature relationships) or there is ...
The most common cause of P0668 (PCM / ECM / TCM Internal Temperature Sensor Circuit Low) is: PCM/ECM/TCM actually overheating due to environmental factors
Typical repair costs for P0668 range from $200 to $1,600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
If the PCM is genuinely overheating, continued driving risks module failure and sudden stalling. If the sensor is merely reading incorrectly, the PCM may unnecessarily enter protective modes reducing power. Have this diagnosed promptly — a failed PCM while driving can leave the vehicle stranded.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0668 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Engine Control Module
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
