P0666
Control Module Internal Temperature Sensor A Circuit
A general circuit fault on the ECU's internal temperature sensor A - the sensor that monitors module operating temperature for thermal protection.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
Common causes
Ordered by how often each turns out to be the cause.
- Internal sensor faultCommon
Parts involved
- ECU Internal Temperature Sensor A
P0666 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.