New problem on my 2006 m35. Radio-navigation screen goes out and climate controls stop working.
Had this happened once before, checked the electrical board to see if any loose resistors (like I’ve read) and everything seems fine.
Bought a used head unit c/d changer with the climate control computer on top and swapped it in. Everything worked fine for a week then today on my drive home it went out again. Screen went black, climate controls locked up and a/c started blowing??
Any ideas????

Diagnosing that stuff without a Consult or other fully capable scanner is a bear, See ATC-45:
https://www.nicoclub.com/service-manual ... %2Fatc.pdf

The AV and HVAC components all have their own private CANbuses which don't talk to the OBD connector, so even with a Consult, all you can get are second- and third-hand codes from the one device on the bus which does talk to the OBD, the AV/Navi Controller behind the glovebox. The problem is, if one of those other devices is crashing one of the private buses (and any one of them can), all you may get from the AV/Navi are a bunch of U codes that aren't very helpful. Since the front display is the one device which is under direct supervision of the AV/Navi with no connection to a bus, I tend to think your AV/Navi would be the culprit, but with the caveat that a crash on the private buses will generally also lock up AV/Navi and lock up or kill the display in consequence. So if a replacement AV/Navi doesn't rectify it, the problem could be any one of the other six devices connected to the private buses.

The crappy thing is that it works then doesn’t work. Total intermittent problem.
I will definitely check the nav computer.
Thanks!!