Not saying the autoparts store is always the best option, but when you already know the problem and solution (like left gas cap off) and you just want it cleared it's an easy and cheap way to go about it.
For those with Volkswagens this is the best tool available for this sort of stuff.
http://www.ross-tech.com/Can also log Data while running/driving, for example boost pressure and requested boost. It will check timing, and countless other things, it's way more useful than I know what to do with yet.
Grigg
