DTC P0116: ECT Sensor Circuit Performance: Description
WARNING: This page is about a different car, the 2002 Saturn LW300 and 2002 Saturn L300. However, it is still accessible from the selected car via links, so may be relevant.
Engine Coolant Temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. ECM supplies a 5-volt reference through a pull-up resistor(s) to sensor, which is connected to ground. When sensor is cold it has a high resistance (high signal voltage at ECM). As sensor temperature increases, its resistance decreases (low signal voltage at ECM). ECM uses signal voltage to determine engine coolant temperature. ECM calculates a modeled temperature using start up ECT, MAF, MAP and engine run time and compares this value to ECT sensor signal. DTC sets when ECT deviates more than a calibrated value from ECT modeled temperature.