Hi. I just got an 2006 A4 Quattro. I bought an aftermarket radio but havn't had it installed yet. Someone had mentioned to me that the diagnostics for the car runs thru the stock radio and installing an aftermarket can cause problems. I purchased the wiring harness for my car (metra harness #70-1787) as well as the Metra steering wheel control harness. The radio is a Kenwood DDX-371. I'd like to get the radio installed this weekend so uf anyone can let me know of any known problems please help me out.. Thank you