did a search and notice people had similar problems but not the same one as mine:

I have had a 2002 q45 for a couple years now. recently, the radio stopped turning on when I press the radio button. i figure i'll try to turn it on with voice control; instead i just get a message on screen saying "voice not ready". navi and everything else seems to work fine.

anyone has any clue? help would be appreciated!

Do you have video for the radio ? If not I just went through this very same problem. It was a low voltage at 12v. The tape player had to e replaced . Te ape also acts a the av unit I believe it is ,or the control unit I don't recall which one but that's it. I read another post of someone else who had he same problem and he also said the same thing. Thats what I told the person that fixed mine 700.00 later.. There available on line . videosevicestop.com

the video shows nothing when i hit the audio button, but i can navigate the navigation screen fine.

the link you provided is broken. are you saying it costs $700 to fix this problem?

It ost me 700. But I found a mechanic that that did it on his time. Knowing what I now know I would replace the player myself. There is enough info available on these sites along wit the fsm (factory service manual) to do it.

just ran the self diagnostic and the control unit and the audio unit show up yellow O_o

I have been looking for a fix to a bad Nav control unit. All aspects of climate control, radio, rear camera, and NAV dont work intermittently. As car heats up unit comes back working fine. But at a cold start nothing. I have read several posts and all fingers point to bad voltage control unit in trunk. There was a post on a guy to send it to in Duluth GA for repair. I called and he wont take it without the car. Does anyone have any other ideas short of taking it to dealer?

I had the same problem with my 2002 Q45 and wanted to chime in. Radio stopped working and when I pressed the voice button it said voice command not ready. (everything else worked) I bought a 2004 M45 tape deck from ebay for $44 and everything works again. Took 15 minutes to remove and another 15 to install. The new deck is black instead of chrome. a few things I noticed: lights on the tape deck did not function when radio did not work, backup camera does not function when tape deck is out. Everything works now, part was over $1500 from Joe. Thank you ebay.

I have 2002 Q45 base model , everything working one day next day air stuck on high and radio and climate controls , voice , not working , kept pushing climate button eventually air went to low . All buttons did not work , but air stayed on .It was the AV module for for the center control bezel. Got used one off eBay, complete center bezel with controls except this one has a combined am/fm button and sat button, Seller said it fit 2002, I’m thinking 2003 , cost was 248.00 Everything working after installed.