P0117Powertrain
Powertrain · SAE
Engine Coolant Temperature (ECT) Sensor Circuit Low
Meaning
The ECU detects an ECT sensor voltage that is too low, which corresponds to an implausibly hot temperature reading. This is typically a short to ground or a failed sensor.
Common causes
- Failed ECT sensor (resistance out of specification)
- Signal wiring shorted to ground
- Corroded or loose connector, or bent pins
- Damaged wiring chafed against the body
- Faulty sensor reference ground
Symptoms
- Check-engine light on
- Cooling fans running early or staying on continuously
- Over-rich mixture and rough running
- Increased fuel consumption
- Possible cold-running driveability issues
Severity
Moderate: the ECU uses a fallback value, but fuel economy and fan control should be corrected promptly.
What to do
- Read the live temperature value and compare it with the actual engine temperature
- Measure the ECT sensor resistance and compare it against the manufacturer's table
- Inspect the signal wiring for a short to ground
- Replace the sensor if out of specification and clear the code