What is wrong with the fuel level sensor?

The fuel level sensor isn't working. Check engine light is on, I took it to Auto Zone and had them plug in the computer and it said the problem is the fuel level sensor. It also said a possible cause is a bad connection. Has anyone else had this problem and was it the sensor, a fuse, or relay? If it is the actual sensor I will wait since it will be a costly repair, however if one of the other or another easy fix I will just take care of it. Thanks.