DTC P0125: ECT Excessive Time To Enter Closed Loop Fuel Control: Description

Engine Coolant Temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. PCM supplies a 5-volt reference voltage through a pull-up resistor to sensor, which is connected to ground. ECT sensor resistance is high when coolant temperature is cold. Resistance drops when coolant temperature increases. PCM reads voltage drop on signal line to determine coolant temperature. DTC sets when engine coolant temperature has not reached calibrated temperature necessary for closed loop fuel control.