Get yourself a VAG specific scan tool. VCDS Lite is cheapest, if you have a Windows laptop. Under a tenner for a KKL lead, download is free.
Can be challenging to get working, and in it's free version, very limited, but will give you all fault codes from all controllers.
OBD Eleven is a good alternative, and in it's basic form, under £40, as long as you have an Android phone.
I prefer VCDS, but I'm warming to OBD Eleven. The Bluetooth connectivity, (no cable), and the ease of emailing scan results to yourself are very convenient.
Either way if you have an FSI, a VAG specific scan tool, should be your first purchase, even before you buy the car.
Mac.