Try lightly sanding the filler neck (put a rag in the opening to catch any crap) where it seals to the gas cap, and apply a thin coat of grease to see if it seals the cap. Probably something of a more significant nature, but always good to check the easy stuff first.
I have had Evasp codes from poor sealing caps before. Generally speaking the first thing I do is go to dealer and get another cap and try it first. The rubber seals do not last forever.
Here with air-care (emission testing stations) they also have a machine that pressure tests the cap. Not uncommon to have them fail. Try a new cap!