I think one of the cheapest ways is ODB11 - It's a great little phone app and dongle and is a nice addition to VCDS and does many things. I keep mine in the ashtray for checking any bits and bobs when about.
First version is Android only, £35 for the basic device - I unclipped mine apart and added a pull cable, but i would probably go for the £44 easy remove version as the A8 D3 ODB port is tricky to remove without.
https://obdeleven.com/en/home/25-obd...423005110.html
Pro licence adds £22 but is needed for more than viewing. Credits are a bit of a pain, but i've never bought any and logging on a few times adds them etc
It'll do brakes and so much more. VCDS is better but also WAY more.
There may be an LCD based scan tool type thing that will do it, but they tend to be pretty limited