OBD II Protocol?

[Keeno21]

Does anyone have any idea which protocol (ISO9141, CAN, KWP 2000 etc.) that VAG vehicles (specifically the 9n) use?

I've got a generic code reader that should, according to Ross-Tech, scan the engine fault codes. However it hasn't been able to detect the protocol on either my old A3 or my current 9n pd100, but does pick up my gf's Fiat 500. I just wanted to make sure that it is the reader that's at fault before I lay into Sealey on the phone...