Out of nowhere this happens to my 04 tl.

When radio is on, touchscreen or navi related buttons do not work. Also the display above the navi does not display track/radio info. Hvac info , clock is OK. When I turn the radio off, I can operate navi no problem. Any ideas? This is weird.

 

most likely its an issue with the navi drive in the trunk since it controls all the stuff that you mention.

 

I followed all the continuity test from the service manual, all came out ok. The one thing I could not do is substitute for known good modules/panels. It seems though it might be the display panel control unit. Did anybody ever replace it?