How do I fix a P0442 code in a 2012 Hyundai Accent? I replaced the fuel cap, but after the Check E L pop up again same trouble code  ?

If the filler neck isn't rusted and you think your gas cap is ok, the charcoal canister vent valve can be the problem. Do a search on youtube for that code on your car and see if there are any common fixes for it.

So I googled the error code and got this:

The P0442 error code is an evaporative emission control code and is an indication of a small leak being detected in the evaporative emission system. ... The evaporative emissions (EVAP) system is used to prevent fuel vapor from escaping into the atmosphere. Code P0442 stands for EVAP system small leak detected.

Keep in mind that I am no mechanic, but by reading this it sounds like you may need to overhaul the EVAP system and see where the leak is if the cap replacement didn't work, as it sounds like the leak is elsewhere. 

LOL, look at me talking like I know all about this stuff. Truly tho, I hope you can get this fixed. Good luck.