Why the fan of a nissan sentra 2003 stop working. what it can be can some body tell me.

link on relay
https://www.justanswer.com/nissan/2sn3q-2003-nissan-sentra-gxe-relays-the-hood-compressor-push-button.html
two fuse boxes link
https://www.youtube.com/watch?v=yIB4rlYwpjo
owners manual 03 sentra
https://justgivemethedamnmanual.com/nissan/2003-nissan-sentra-owners-manual/
Hope something here can help you

YOU CAN BUY THERMOSTAT AT ANY AUTO PARTS STORES OR DEALERSHIP.

Replace just the TPS Sensor (throttle position),
not the entire throttle body, as you may have been told

Educate Yourself

Be careful,you will be sold something
you don't need

you need a fan switch it screws into the engine block or the bottom of the radatior tells the fan when the engine needs cooled

Maybe but Check to see if the radiator is full and the overflow tank for the radiator is full. If it's OK take the car to auto zone or Orilys (Schucks) and have them pressure test the cap, if the cap passes the pressure test then make sure there is nothing blocking the radiator and if it has an electric fan be sure it is plugged in. In the tune up procedures some cars require the fan to be disconnected.

Could be the fuel pump or throttle body.

I would attempt to check the fuses.

good day Sir, try this link nissan sentra 2003 owners manual

No, it should only turn on when the temperature switch tells it to. On a hot day you may hear it running even after shutting off the engine. The fan is set up so that when you are moving at enough speed the fan shuts off to save energy, when you slow down or stop the fan should come on to maintain airflow. If you check it at this point yes it should be running. When you start it cold the fan will not turn on for maybe 10 or more seconds when the engine starts to warm up. Hope this helps.

Things to be concered about; 1.) the fan never seems to turn on. This will cause your engine to overheat when you stop.
2.) Your heat is not working. The heat going away can be a sign that you antifreeze is low and that you are about to overheat.

Chances are it is not the coolant temp sensor. The sensor is located right above the alternator, if you have the smaller engine. I wouldn't touch the sensor if you don't have a check engine light on.