hi guys so my mate has a 2011 Audi A7 and recently he has got rid of his dpf and has put a downpipe, sounds awesome for a 3.0 tdi. so now after hes done this hes got a gearbox malfunction no reverse gear but still able to drive. we don't know why this has happened. also the car only drives on gear 1, the paddles don't let him change up. its a real pain. I've used vcds on his car and scanned some fault codes up and it says valve 4 in transmission part 2 code is p174f. Now theres also another problem with his parking brake, it says on vcds no communication with parking brake control module, i try go on the parking brake bit on vcds and it says no response with controller. honestly i don't know what both these problems are can someone help me
