I'm having a issue with my auto dimming mirror on the drivers side and wondered if anyone knows what sensors trigger this to come on. Or if it can be triggered through 4scan. The dealer said it's about a 30min job to test as they have cover up multiple sensors and let them time out. They also said glass is not part of the warranty and didn't get my argument that it's electronics that are the issue not the physical glass. I assumed it came on with the dash sensor but can't confirm as it no longer works

 

It's triggered by the rear-view electrochromatic mirror sensor. The front facing sensor on the mirror must be dark (electrical tape should work) and the rear facing sensor must sense a glare condition (flashlight at an angle), and the mirrors will be triggered to "dim".

 

My .02 cents, Its the rear view mirror sensor..

I know this because one day I placed my window shade on my dash which covered the sensor and darkened the inside. I immediately noticed that the mirror had dimmed and could tell that it was active. While i sat in the vehicle, i decided to remove the connector from the rear view and the mirror UN-dimmed.
I would try and see if you can get it to activate this way.. How do you know that its not doing whats its supposed to? There was a time I thought it was not working but it was..

 

Honestly, if your mirrors are positioned properly, the tinting feature becomes a moot point. The only time it really comes in handy is if you get a driver in the left lane that insists on riding on your rear quarter panel. That can be resolved with the brake or accelerator, though.

 

I've noticed when I have the truck in the barn, with the overhead door open, on a bright day, the left mirror is dimmed when I start the truck. Once I get in the sunlight, the mirror loses it's blue tint. Just an FYI.

 

Mine dims with the rear view mirror. However, since my windows are tinted in addition to the factory tint, it isn't too often my mirrors dim.