P0118Powertrain
Powertrain · SAE
Engine Coolant Temperature (ECT) Sensor Circuit High
Meaning
The ECU detects an ECT sensor voltage that is too high, which corresponds to an implausibly cold temperature reading. This typically indicates an open circuit or a failed sensor.
Common causes
- Failed or internally open ECT sensor
- Open signal wiring (broken circuit)
- Faulty, oxidised or disconnected connector
- Missing sensor reference ground
- Low coolant level leaving the sensor exposed
Symptoms
- Check-engine light on
- Hard starting, especially when the engine is warm
- Incorrect mixture and rough running
- Cooling fans may fail to run
- Increased fuel consumption
Severity
Moderate: with the sensor always reporting cold, the fans may not engage and the engine can overheat.
What to do
- Read the temperature value: a fixed, very low reading points to an open circuit
- Check the coolant level and condition
- Inspect the wiring and connector for an open circuit or poor contact
- Measure the sensor resistance and replace it if out of specification