DTC P0115: ECT Sensor Circuit: Description

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. DTC sets when calculated accumulated airflow exceeds predicted accumulated airflow when engine coolant temperature has reached a calibrated temperature (more air will flow through a cold engine than when engine is warm).