my auxiliary doesnt even show up on the car
one mechanic told me that maybe there is a cable that somehow disconnected or i need a new navigation system

I have just got my car back from the garage and all the eceltrics have been disconnected and reconnected. It is asking for a 4 figure code for the radio/cd/sat nav. I have the code but can't find out how to enter the code. There is nothing in the "Audi Navigation System Plus" Operating Insructions that I can see.