You may find yourself in a sitution where your CD changer no longer seems to be functioning and the display on the radio head unit reads "CDERR" when you try to access your CD changer. Additionally, when you press the magazine eject button on the CD changer nothing happens.
Don't panic, you may just have a jammed CD or loose CD that is outside of the CD magazine. When this happens your CD goes into shutdown mode where it seems to be dead. Some dealers provide their customers with a wallet sized card with instructions on how to deal with this problem. My dealer didn't but luckily for me, one of my A4 Internet buddies did have such a card, and my CD changer nightmare was corrected without spending a single penny.
For those of you still covered by the factory warranty, it may be best to just have the dealer correct this situation. They will do so free of charge no matter what the problem is. For those of you with expired warranties, keep reading.
The image below is a scan of the front and back of the CD Eject Manual Override Card. When your CD changer acts dead, as described above, follow the instructions on this card to manually eject the CD magazine. (Since you do not have the actual card, use a wallet size card that is about half the thickness of a credit card, a stiff business card may actually work). You will hear a slight click, and the CD magazine should eject with ease. If it does not, you may have a CD which is jammed half way out of the magazine (Go to Paragraph B). Even if the CD magazine ejects with ease it is still important to check whether or not there is a loose CD floating inside your CD player (Go to Paragraph A).
A) Your magazine has popped out manually with ease. Use a flashlight to inspect the inside of the changer. Check for a loose CD inside the CD changer. This loose CD will be completely free and will probably be resting on top of the CD player mechanism. The CD in the player mechanism appears to be inside of a metal sandwhich, and it will be obvious if there is a loose CD on top of the player. Use needle nose pliers, or other means to lift and remove the loose CD. Then re-insert an EMPTY magazine. You may hear the CD changer jump back to life at this point. Let it do its thing, and when it stops, press eject magazine button, and the CD in the player will be loading back into the magazine, and then it should eject as normal! Congratulations, you are back in business!
B) What to do if the magazine does not manually eject freely. Again, don't panic. Remove the CD changer completely from the car, and unscrew the CD mounting bracket from the changer. It is now possible to remove all of the screws on the external housing in order to lift off the black sheet metal housing of the changer. You should immediately see your problem. In my case, I had a CD which was stuck halfway out of the magazine. My CD changer tried to stuff two CDs into the same slot. Using a pair of needle nose pliers, I carefully removed the trapped CD, and placed it into an empty CD slot. Then the magazine manually ejected easily. I then placed the black sheetmetal cover back onto the CD changer, plugged the changer back into my car, turned on the radio, and then followed the rest of the instructions on CD Magazine Eject Manual Override Card. Don't forget that you have to reinsert and EMPTY magazine back into the CD changer.
Special thanks to Don Pavlik for the card scans and helping me through my CD changer difficulties.