2011 Crewmax CEL turns on and off

I posted this in the wrong forum initially my mistake!

I get this code every time



p0420 $07e8


It's odd because it will throw the code then disappear. I've only had the truck for a couple of months and the one commonalities is that it always happens with a new tank of gas, then about 1/2-3/4 of the way down the light turns off. Fill it up...within a day its back on again.