When the P0119 OBDII fault code is set, it is because the vehicle’s computer has detected an intermittent signal from the ECT (Engine Coolant Temperature) sensor. The PCM always monitors the ECT Sensor for a reference signal, which is 5 volts.
This sensor has 2 wires, one for reference voltage and the other for ground. It is a negative coefficient sensor. For example, when the temperature increases, the resistance decreases. When there are variations in the resistance, it is due to changes in the voltage, which are recognized by the PCM as changes in the ECT sensor. It is worth mentioning that there are other models of these sensors that have 3 wires, being the third wire for the input signal supply to the meter. Although the location of this sensor varies by manufacturer, it is always threaded into an engine coolant line.
If the PCM receives signals from the ECT Sensor for some time and these signals prove to be intermittent or erratic, the Check Engine light will illuminate next to this code.