the stealership has a code reader they plug into a jack under your dash that reads fault codes. once they run that they will decipher the code and tell you what they think is wrong. then they start replacing parts until the code goes away. $3 grand later your car is fixed with a bunch of parts that didnt need to be replaced.
or you can go to autozone and let them scan it for you for free and they will tell you what they have as a code. granted this probably wont be as specific as VW could guess, but its a start. Once you have the gouge from autozone, get on the internet and do a google search for the problem on your car, any recalls, and also check volkwagen forums FAQ like
www.vwvortex.com
good luck.