There's two. One for the Engine Computer and one for the dash gauge. The one for the computer will have two wires in its connector. What is the symptom? The sensor for the computer is fed with 5.0 volts. It will pull the voltage down depending on temperature. Anything between 0.5 and 4.5 volts is acceptable. Anything outside that range will set a fault code. These sensors give very little trouble. Also, you can not rely on resistance readings alone to tell if they're correct. Ten sensors will read ten different resistances at the same temperature. The computer uses different strategies to test the sensor. One thing it does is compare the reported temperature of the coolant temperature sensor to the intake air temperature sensor after the engine has been off for at least six hours. The two are expected to be the same temperature. A sensor can have scale build up on it that sort of insulates it from the hot coolant. That can make the radiator fan slow to turn on. The computer should turn the fan relay on at 212 or 220 degrees, I can't remember for sure.