This is a video of the engine coolant temperature (ECT) sensor. This video explains how the ECT sensor works. As the temperature goes up, the voltage goes down. Only two terminals are used, the ECM ground and the 5V reference terminal. The ECM ground is connected to the pin number 5 and the 5V reference coming from the ECM/PCM. Here is the video:
To test this sensor, turn on the machine key, disconnect the ECT, connect the multimeter between the battery negative and the signal wire. The voltage should be 5volts, then reconnect the sensor, measure the voltage between signal line ground.