P0666: Control Module Internal Temperature Sensor A Circuit
What to do
Usually driveable with no symptom. The sensor is inside the control module, so there is no separate part to replace; the fault matters mainly because the module's own thermal protection is compromised.
What this code means
A circuit fault on a control module's own internal temperature sensor. Modules monitor their own temperature so they can reduce output before heat damages them, and this concerns the sensor doing that monitoring rather than the temperature itself.
Because the sensor is inside the module, there is nothing external to test or replace — this is a module-level fault, though a mild one while temperatures stay normal.
Likely causes
Start here
- Failed control module · specialist
Less common
- Water ingress into module · specialist
- Low system voltage disrupting communication · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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