DTC P0125-00: Insufficient Coolant Temperature For Closed Loop F/Control: General Description

The Engine Coolant Temperature (ECT) Sensor is located in the engine coolant passage of the cylinder head for detecting the engine coolant temperature. The ECT Sensor uses a thermistor whose resistance changes with the temperature. The electrical resistance of the ECT Sensor decreases as the temperature increases, and increases as the temperature decreases. The reference 5V in the ECM is supplied to the ECT Sensor via a resistor in the ECM. That is, the resistor in the ECM and the thermistor in the ECT Sensor are connected in series. When the resistance value of the thermistor in the ECT Sensor changes according to the engine coolant temperature, the output voltage also changes. During cold engine operation the ECM Sensor increases the fuel injection duration and controls the ignition timing using the information of engine coolant temperature to avoid engine stalling and improve driveability.