Engine Coolant Temperature Sensor

Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance of 100,000 ohms at -40°C (-40°F). High temperature causes a low resistance of 70 ohms at 130°C (266°F). PCM supplies a 5-volt reference signal to ECT sensor through resistors in PCM and measures voltage. ECT signal voltage will be high when the engine is cold and low when engine is hot. By measuring ECT voltage, PCM calculates engine coolant temperature. Engine coolant temperature affects most systems that PCM controls. Scan tool displays engine coolant temperature in degrees. After engine start-up, temperature should rise steadily to about 85°C (185°F). It should then stabilize when thermostat opens. If engine has not been run for several hours (overnight), engine coolant temperature and intake air temperature displays should be close to each other. A hard fault in ECT sensor circuit will set DTC P0117 or DTC P0118. An intermittent fault will set DTC P1114 or DTC P1115.