The nav on my NEX 5100 won't follow the road and when I was going do the interstate the other morning was basically thinking we were spinning in circles. You can't hardly use the nave because everytime it finally catches the road again it keeps stating the miles till next turn, etc and obnoxious to have that play every handful of seconds. Installed in June and installed the firmware and map updates then too. The GPS antenna is mounted on the little magnetic stick-on pad that was included with it and is on top of the vent ducting which is just left of the headunit and about an inch below the dash top.

 Here is a video showing it:

https://youtu.be/SJ_Gge6a_14

Searching around looks like these guys has similar problems. Anyone have a fix without requiring replacing the unit?

http://avic411.com/index.php?/topic/80538-8000nex-losing-me-on-map/?hl=road

Put your antenna on top of the dash, not inside of it.  I understand it is only plastic above the antenna, but it is just another material dampening the sat signals.  I have my antenna on top of the dash in the corner by the passenger A pillar with a clear view of the sky, and since installation it has not lost me. Even recalculating when I deviate from its route is within seconds.

I never lose satellites though, show 9-10 at about any given time. Instructions even say just under the dash.