The ECT Sensor (Engine Coolant Temperature) changes its resistance according to the temperature. It has two wires: one of the reference signal, which is 5 volts, which is provided by the PowerTrain Control Module (PCM), and the other cable is from the ground circuit.
When the coolant temperature changes, the resistance also changes in the ground signal to the Powertrain Control Module (PCM). If the engine has a low temperature, the resistance is high, while when the engine temperature is high, the resistance decreases. If the PCM detects that there is a condition or voltage outside the range, that is, it can be high or low when in fact it is not expected, the code DCT P0115 OBD II is established.