PCM/ECM/TCM Internal Temperature Sensor Circuit Malfunction
The P0666 code indicates a fault in the internal temperature sensor circuit of the Powertrain Control Module (PCM), Engine Control Module (ECM), or Transmission Control Module (TCM). This sensor monitors the module's internal temperature to prevent overheating. A failure can cause the module to misread temperature, potentially leading to performance issues or module damage.
01. Most Common Causes
- Faulty internal temperature sensor within the PCM/ECM/TCM
- Damaged wiring or connectors to the sensor
- Corrosion or poor electrical connections
- Failed PCM/ECM/TCM module
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine performance issues (hesitation, stalling)
- Transmission shifting problems
- Overheating of the control module
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Inspect the PCM/ECM/TCM connectors and wiring for damage or corrosion.
Step 3: Test the internal temperature sensor circuit with a multimeter per manufacturer specs.
Step 4: If sensor and wiring are okay, consider module replacement or reprogramming.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the module may overheat, causing further damage or sudden loss of control.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. If the module needs replacement, it can range from $500 to $1500 including labor.