Hi, i've got a Audi Q7 3.0 TDI 2008 S-LINE v6  mmi 2g basic

my cd changer has been replaced to another one exactly the same, and there is no sound, there is sound from my parking sensors etc... but no sound from cd changer like radio, music or nothing. i am wondering if you need to code the new cd changer to the engine?

The units are coded to the car to try to make them useless if stolen. 🤔 I think the head unit and the mmi screen are a pair so might be why you aren’t getting sound but I think the mmi usually says “no cd” rather then plays no sound though. I had a problem with my mmi screen not long after I bought mine and the garage said they had replaced the screen and the cd changer. So if you can try the 09 mmi screen with the 09 cd changer it might cure it but I’d be tempted to run a scan on vcds before paying anymore money out. I dare say the scan will probably say it’s in “component protection” mode. Which as far as I’m aware only audi can remove with VAS software linking back to Germany. Audi probably won’t want to help you code a 2nd hand unit and try telling you only new units can be coded.