I have 2009 A4 Avant. The right rear door will not lock with either the key fob or by hitting the interior lock switch. It I manually lock the door via the access point on the door jam, the door will lock and will then unlock with the key fob but will not re-lock with the fob etc. Fuses OK. Note that the confirmation lock tone will chime if the door is locked manually but not if the door is not locked manually. Seems to me this could indicate a faulty sensor in the lock mechanism. How is this accessed? Any other ideas?

 

Have torn this down all the way to the lock mechanism and found nothing obvious. Looks like it off the service shop.

 

I have a 2010 Avant with the same issue. I used the manual lock on the jam and it now stays locked when I lock and unlock the doors remotely, which I can live with but would prefer to have it fully functional.
What did you arrive at for a repair?

 

Try this link in this forum.
https://www.audiforums.com/forum/b6-...-179267/page3/
This is a well documented fix. If you are handy, it is a $0 repair, just some labor. Or if you want to send me the module, I can repair it for you.