What does it mean?
P1116 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Engine Coolant Temperature (ECT) Sensor 1 Circuit Range/Performance Problem .
Symptoms
- Engine takes an unusually long time to warm up and the gauge stays low
- Weak cabin heat in cold weather
- Check engine light on, often after a long motorway run or several short trips
- Higher fuel consumption because the module keeps a cold-engine fuelling strategy
- Prolonged fast idle and a rough feel while cold
- Cooling fans behaving inconsistently
Likely causes
- Thermostat stuck open, so the engine never reaches or holds its normal operating temperature
- Low coolant level or a large air pocket around the sensor tip
- Sensor that has drifted with age and now reads a few degrees off across the range
- High resistance in the signal or ground wiring shifting the whole reading
- Wrong sensor fitted with a different resistance curve
- Cooling fan running constantly because of a separate fault, over-cooling the engine
- Head gasket or combustion gas leak disturbing coolant flow past the sensor
How to fix it
- Check the coolant level and bleed any air from the system before electrical testing
- Compare coolant temperature with intake air temperature after an overnight soak; a large split points to a drifted sensor
- Graph the warm-up from cold and note whether the temperature rises steadily and levels off at the normal value
- Check the thermostat operation by watching the upper hose warm up and comparing it against the coolant reading
- Measure the sensor resistance at two known temperatures and compare it with the manufacturer's table
- Voltage-drop test the signal and ground wiring, since added resistance shifts the reading without breaking the circuit
- Replace the thermostat or the sensor as the tests indicate, then confirm a normal warm-up curve and stable operating temperature