there are two water temp sensors. a one wire and a two wire. the one wire is for the dash gauge and the two wire talks to the computer. what was the P code thrown? the sensors go bad over time. if it's the two wire sensor, the truck will run rich. if it was the other, the you would get an almost instant hot read, or it wouldn't lift the needle depending on fail open or short. you make certain of a failure with a multimeter. the two wire test is more complex, but still need a meter. either one can leak.