P0666Control Module Internal Temperature Sensor A Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- Control modules measure their own circuit board temperature with an internal sensor to protect output stages (overtemperature is P0634) and, in GM transmission modules, as a substitute for fluid temperature. In GM's 6T70/6T75 and related automatics the sensor sits in the transmission module inside the valve body, with no external wiring – so the repair is practically always the module or valve body assembly. P0666 is the general circuit fault of this sensor A. No manufacturer table available to us uses P0666 itself – GM splits the circuit faults into low (P0668) and high (P0669), plausibility is P0667. Expect a warning lamp and, in a transmission module, changed shift quality because a substitute temperature is used.
- What you may notice
- Warning or check engine light
- Changed shift quality (substitute value)
- Possibly transmission fluid temperature codes
- Likely causes
- LikelyModule faulty internally (temperature sensor or measuring circuit)
- PossibleMoisture or corrosion in the module or valve body
- RareSupply or ground problems of the module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €300 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.