I just purchased a 2004 Lexus LS430 with the Mark Levinson sound system. On purchase, the navigation touch did not work. I am not even able to touch I agree on the unit. No sound plays through the radio, CD changer, not the cassette deck. If no sound plays, I would look at the amp, correct? Yet, if it was the amp, would the screen not work? To confuse me more, voice controls work and the little lady can actually talk to me! So, would the voice recognition work if the amp was flogged or would it be the navigation head unit? I'm wondering if anyone has had both systems fail? I plan to remove the amp today, and clean it out, put some dielectric grease on the connectors, and put it back together in the hopes the board was shorting on dust or the connectors where loose. Let me know what everybody else thinks!

 

Sounds like the amp is fine if you can hear the replies to the voice commands.
I would suspect the touch screen itself.
What happens if you select a different screen with one of the non-touch buttons such as Climate or Audio?
If you can select them, does touch screen work on those screens?

 

Selecting the other options in the menu via the buttons also does not allow me to use the touch screen. I planned to replace this part to begin with but my worry is the audio not coming out of the speakers from any source. I got this Lexus for under 5k so I'm okay with spending the dollars on it to get it up to par. Thank you for your reply. I will update the board with any new discoveries

 

My navigation system failed about 5 months ago on my 2001 LS430 (305,000 miles). I found a used, functional replacement on ebay for under $200. Actually came from a Toyota later year so I got an upgrade in the process.