2011 A4 - What is a "radio module"?
 

My radio/cd/etc stopped working. It caused my display to go out.

I own a 2011 A4 B8, no navigation, just the basic CD player, some ipod connector in the glove box with a cable that i can change out, and blue tooth for phone only.

when I turn on my car, the CD player lights (to the right and left of the insert slot) just blink. I removed the unit and the fuse in the back seemed good.

I took it in to the dealer and they said that it was the "Radio Module" and that it would cost $500.

What exactly is the "radio module"? is the the entire head unit?

any help on how to diagnose this?