On my onstar rearview mirror the mirror dimmer button seems to turn on by itself, my non-Navi rearview mirror did not do this,
am I missing something?
Is there a difference in the mirror auto-dimmer for the onstar mirror and the non-onstar mirror dimmers??

 

Do you mean like when you drive into a dark area from a light area that green light on the mirror dims? I've got the onstar like you and thats what i noticed as well.

 

The dimmer indicator button on the left side of mirror lights up green (seems to turn on by itself) , this means it is dimming, but I never touched the button, On my other CL, the green light came on only when I pushed the button to turn it on. Is it automatic on the onstar version??

 

On my '01 CLS, the dimmer would stay at the setting I last set it at (on/off). On my '03 CLS with OnStar, the dimmer doesn't remember my last setting and is always on by default.