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auto dim rear view mirror

8K views 13 replies 7 participants last post by  pauline 
#1 ·
The auto dim rear view mirror is annoying me to no end. I actually like seeing who is behind me (old habit from my CHP frequent flyer days). Yes I can turn it off... every time. Has anyone found a way to switch it manual mode?
 
#5 ·
You can cover up the little light sensors. Then it will never think you have a bright light shining on it, so they will never dim. (I think that's right. I seem to recall that covering them leaves it in 'undimmed' mode rather than dimmed.)
 
#7 ·
This discussion made me wonder about my '06, so I just went out and experimented with it. Per the owner's manual, the mirror does go into auto dimming mode each time the ignition is turned on, and that feature apparently cannot be turned off. So then I tried covering the rear light sensor with my finger and the mirror in auto dimming mode, and it immediately got lighter. However, with the mirror dimmed, leaving the rear sensor uncovered, but covering the front sensor (on the back of the mirror on the left side as you face the mirror) causes it to get even darker. This doesn't make sense to me, but I went through it several times with the same result. This all took place in my garage in the mid-afternoon, with the garage door open or closed making no apparent difference.
For me, the dimming mirror is an asset due to a tendency of some drivers in larger vehicles to tailgate smaller ones. Here in So. Calif. we also seem to have a lot of drivers who favor running fog or driving lights regardless of any condition requiring them.
 
#8 ·
Yeah I have a '06 too and it comes back on, thought it was when I switched my headlights on, but according to Roger its when the ignition is turned on I guess.

I used to switch it off, but I'm in the same boat as Roger, plus there's a lot of idiots here in California that don't know the difference between regular headlights and high beams.. it's come to help me more than hurt me. Now if only the side mirrors could be dimmed.
 
#9 ·
Phish,
Yes, it is ignition switch rather than headlight switch activated. I don't use the "always on" feature for the lights, so mine weren't on when I was checking out the mirror.
Regarding the outside mirrors, the electrochromic (auto-dimming) on both outside mirrors came standard on my '02 Lexus, and I had a similar driver's side mirror on my '92 Cadillac, so the technology has been around for a long time. I have an idea that Toyota didn't put it on the Prius in order to keep the price down a bit. I'm guessing their focus groups didn't put a high priority on that option when the cost was factored in. Actually, the way my outside mirrors are positioned, I don't have a problem with lights from the rear. I agree with you though regarding the highbeam issue. Lots of bullies out there on our freeways!
 
#10 ·
From what I recall, the sensor on the front of the mirror determines if it is night or day, the one on the back figures out if it needs dimming or not.

So if the one on the front is bright, it knows that it's day, so it doesn't need to dim. If the one on the front is dark, then it will dim if it detects rear lights. That was my thinking, if you darken the rear sensor, it will never know that you have bright lights shining behind you.

(Where "front" and "rear" mean in relation to the car.)
 
#11 ·
Well, I guess it depends how tall you are. The bar across the back window blocks the super annoying tailgaters for me.
For any normal drivers, I'm used to using their lights to figure out where they are in one quick glance. Sounds like I have to get used to turning the sensor off everytime.
If anyone hears of another 'push the odometer, turn car on/ off, get out turn around three times' hack, please post it.
Thanks everyone!
 
#12 ·
The dimming mirror is comparison based. It uses the front sensor to determine the ambient lighting that the mirror is going to compensate for. The rear sensor is obviously for sensing the amount of light coming in from the rear, i.e. somebody's headlights.

The mirror will be undimmed at night if there is no light behind you to tell the mirror that light from the rear of the vehicle is greater than light in the front. As such, if you have nobody behind you at night, and let's say the sky is clear and the moon is full, you should have a clear rear view of the passing scenery.

The mirror becomes "grayer" when light from the rear exceeds the ambient light from the front of the vehicle. This dimming function is totally electrochromatic, and not mechanical, as a side note. Early auto dimming mirrors were mechanical in that a servo motor would tip the mirror down to dim it, in the same manner as you would manually.

To solve the issue of the mirror dimming at night when it is not desired, I believe if you take a small piece of black electrical tape and cover the rear facing (mirror side) sensor, the mirror should never dim, because the rear sensor always thinks that there is no light coming from behind the vehicle.
 
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