I have been searching a few forums for information on how to see if my car has a DPF or not, there is a box just after the down pipe but some people say its DPF some say a secondary cat, they talk about certain years having them and codes in the service book but they all seem to contradict each other and i'm getting nowhere.

The car is an A4 2005 (55plate) 3.0 tdi quattro (204) engine code BKN

Any help will be greatly appreciated