P0669Powertrain
Powertrain · SAE
ECU Internal Temperature Sensor — High Voltage
Meaning
The ECU has detected that the signal voltage of the internal temperature sensor within the control module exceeds the maximum acceptable threshold. A high voltage corresponds to an unrealistically low temperature reading or indicates an internal short to supply voltage in the sensor circuit.
Common causes
- Internal failure of the temperature sensor integrated within the ECU
- Internal short to the reference voltage inside the ECU
- Problem with the internal reference voltage of the ECU (value too high)
- ECU supply voltage out of specification (above normal)
- Faulty internal acquisition circuit inside the ECU
Symptoms
- Check-engine light (MIL) on
- Possible ECU protective mode activation
- Anomalous engine behavior unrelated to other codes
- Sometimes no noticeable driving symptoms
- Possible ECU reset in extreme cases
Severity
Moderate to high: a high internal ECU temperature sensor voltage indicates a fault in the reference circuit or the sensor itself; it may compromise the module's thermal management.
What to do
- Check ECU supply voltage (must not exceed 14.5 V)
- Verify correct alternator and voltage regulator operation
- Check ECU connectors for moisture or corrosion
- Verify the ECU ground connection
- If external parameters are correct, proceed with ECU replacement or specialist repair