I finally got my android auto working 100% today, then I hit the mode button on my steering wheel (cycles through av inputs), and voice stopped working. So similar to what everyone else had been saying the voice would try to kick in, no sound, no mic working. I thought it has been working before, yet it now doesn't work makes no sense. Tried restarting 4100nex, tried restarting my phone, no luck. In the end I uninstalled android auto, and reinstalled it again using the apk file I downloaded. Perhaps try downloading the apk version of the app as it worked for me.
FYI: I have a samsung galaxy s5, not unlocked on rogers in Canada. I have an american purchased car and american purchased 4100nex.
I downloaded the apk file and installed it that way.
Btw, a fully working android auto is just unreal! Hope this helps some get theirs working!
Another note: I noticed a difference between using the standard usb 2.0 cable versus the usb 3.0 cable, the 3.0 cable definitely worked better, and has to be used in usb port 2 on the 4100nex.