How do I fix error PO441

Be careful with gas cap replacement. I have a 2006 Hyundai Elantra that ended up having a different type of threading for the gas cap. A mechanic replaced the gas cap with the alleged right one that is listed for the car. It seemed to screw in correctly and then reset the code. The code soon tripped again. After doing all the testing and finding nothing wrong, another mechanic looked closer at the cap while it was on the car and realized it was not fitting correctly. It stumped him because none of his other Elantras had a gas cap that would thread into it properly. He soon found a gas cap from a 2015 Chevy Equinox that had the same two eared kind of alignment and turn to secure the cap in with a proper seal. Reset the code and have not had a problem since.