P0666: PCM / ECM / TCM Internal Temperature Sensor Circuit
MediumPowertrainEngine Electronics
What does P0666 mean?
P0666 is a diagnostic trouble code indicating "PCM / ECM / TCM Internal Temperature Sensor Circuit". A sensor in the engine electronics is reporting abnormal data or has lost communication with the ECU. Sensors can fail due to age, contamination, heat exposure, or wiring issues.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Engine overheating
- Temperature gauge reading high
- Heater not working properly
- Intermittent warning lights
Estimated repair cost
Typical range in Australia (parts + labour)
$100 – $500 AUD
Common causes
- Faulty engine electronics component
- Wiring or connector issue in the related circuit
- Failed sensor providing incorrect readings
- Software/calibration issue requiring ECU update
- Related component causing secondary fault
What should you do?
Schedule a diagnostic appointment at your earliest convenience. The vehicle is generally safe to drive short distances, but the underlying issue should be addressed to prevent it from worsening.
Get a diagnosis for YOUR car
Code P0666 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.