99' Civic DX code P1456
 

I own a 99' Honda Civic DX that just hit 52k a few days ago. For a few months I've been driving with the check engine light on and the dealership said it's got trouble code P1456, but all they did was change the gas cap. It seems to be pressurized inside the fuel tank, when the cap's removed to fill it up there's a quick 'hiss'.

What's the likely problem with that code? I found a list of things online and don't know where to start.

-Matt-
AMGViper