If it was the gas cap causing the CEL, then it will probably go away after the cap is put on good and tight and you run it for a while. Supposedly you can also disconnect the battery for a couple of minutes, and that is supposed to clear the error. If it doesn't go away and the error code was with the EVAP system, then it is probably not the gas cap. I guess it could break, but I wouldn't suspect a broken gas cap unless I knew it had suffered some trauma/abuse. With a fault description of "evaporation emission control system purge flow fault incorrect purge flow", I imagine there are lots of things that could be causing the problem other than the just the gas cap. a loose gas cap is probably the most common and easiest to fix though.So, I'd try disconnecting the battery for a bit. Maybe the problem is already fixed but you just need to clear the error code. If the CEL comes back then you can try the dealer to see what they say. If you're worried that they won't cover it under warranty because of the CAI, you could put the stock intake back in, disconnect the battery for a bit to see if the CEL comes back, and if it does then try the dealer for warranty service. That way you can rule out the easy things before going through the hassle of taking it in to the dealer. That's what I would do, but I'm a self proclaimed non-expert.
http://forums.genvibe.com/zerothread?id=5420 is one of many threads here about mods and warrantiesHow do you like the injen CAI? Did it make a noticeable improvement, install it yourself, etc. Other than the CEL, how's the vibe doing after 18000 miles?