P0668Control Module Internal Temperature Sensor A Circuit Low
- 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. P0668 means the sensor signal is at the low voltage end: GM converts it into a temperature and treats −249 °C or less – a physically impossible value – for 60 s as a fault, with the lamp after two trips and the power-up temperature as substitute. 'Low' refers to the voltage; depending on the sensor type that need not mean a low temperature.
- What you may notice
- Warning lamp
- Changed shift quality (substitute value)
- Scan tool shows an implausibly low module temperature
- Likely causes
- LikelyModule faulty internally (sensor or measuring circuit shorted)
- PossibleMoisture or fluid in the electronics of the valve body
- RareModule supply problem
- 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: €400 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.