My mirror works fine. When it doesn't dim, it's usually because of the distance and the height of the headlights behind me. The sensor can't see the headlights behind me because the rear spoiler is in the way!

 

I have heard a lot of people with the pedestal spoiler complain about the auto-dimming rear view mirror. I assume its due to the height of the spoiler.

Mine works fine in my car. Lights look green in mirror but I have not noticed any green light on