I took off the relay apart, put it back in with the top cap off, and if i push the relay together, the fans turn on. So the fans do work. My question is, What sensor is it that trigger the relay. I replaced one sensor beside the thermostat and it didn't do any good.

Any number of things need to happen- vehicle speed, engine temp, a/c request etc-- so why do you think they are not working???

Fans do not come on until engine temperature (read from a scan tool) exceeds 227 or so....also if a/c is on- it may wait on head pressure to exceed 175psi or so---is your engine boiling over?? or does it just read a little higher than expected on your temp gauge?-- perhaps if you give it a chance they will come on- the system is designed to run the fans as little as necessary- they typically are not on while driving- and only come on after extended idle and warm temps.....

I think they are not working because a sensor is bad. I have waited until the car is warm and they do not turn on. I realized there was a problem when the car started running too warm.