Auto-dimming mirror doesn't work?

My guess is that the rear sensor is being blocked by your rear spoiler, if true, I have no idea how to fix it.

 

If you switch it on/off, do you see any change to light intensity? We've got the same rear-view, and I'd pretty much forgotten the settings, happened to look it up a few months back, and yeah: light on means auto-dimming is (or should be) active.

(Editorial, it should be "glare", not "blare", lol.)

Oh, just reading now, I see everytime you turn the car off, then on, the mirror defaults to be auto-dimming on, or at least it should be:

 

Still under warranty, right ?
Have you had additional tint put on the back window ?

I can't tell from the picture but a lot of center rearviews can be adjusted up or down by several inches by using the swivel AT the window mount point. As mentioned, maybe the mirror position is causing it to be "shaded" by the spoiler or by the back of the roof.

Probably more likely that something actually needs to be fixed.

 

It works, just not very well. It's a known issue...

 

Toyota needs to put the sensor on the top edge of the rear view mirror or at least allow the mirror to be rotated upside down - to get the sensor out of the shadow of the rear spoiler. The mirror is a part used by many cars in the US market.

 

Sometimes I find mine takes a minute after lights hit it to "turn"... As mentioned above, I guess maybe it has to be just the right angle.

I wish the side view mirrors would dim, too. When a huge SUV or semi is driving behind me, the dimming rear view is little consolation when I am being blinded by light reflection off the side view!