That means your gas tank isn't airtight like it's supposed to be. P1456 is the code you'll get if you leave your gas cap loose. But there's a bunch of other things that can cause it, too. Mostly I don't think they'll screw up the way the car runs.

Maybe the EVAP line that's supposed to let gasoline vapor into your engine is letting liquid thru, that would make it run bad. But I'm not exactly sure whether that's a plausible way for the system to fail.