I may not have a complete solution for us all...but I was having the same issue where the mirror would fold all the way forward and not stop where it was supposed to when cycled by the power fold button.
I took the covers off both mirrors by carefully inserting a plastic squeegy around the outer edges of the cover and slowly prying little by little until the cover backed out of the housing. * Be sure to not rush this...especially if its cold outside....there are tabs in the housing that can break if you twist the cover, or try to simply pry the top first, or the bottom first, it must come straight off.
I noticed that the spring and hinge for the mirror was in tact and looking good.
then I looked under the mirror where the indexing "cogs" were in the base plate. This plate is aluminum. There is white lithium grease on all surfaces between the plates cogs and the mirror housings cogs. My car, though not that old, but with high mileage, showed signs of this grease being worn out, gone, and in places pretty thick with road grime and build up.
I cleaned everything I could with a bristle brush (old tooth brush could work). A key for me was to "float" the mirror housing so it disengaged from the cogs while cleaning. this way, I could get the space in between the cogs not only clean, but also re-greased properly.
You will notice on the bottom of the housing you took off, it may be dirty and grimy and this needs to be cleaned off too...basically any sliding surface should be as clean as you can get it.
You will notice after a good greasing, that the mirrors move very easily when pushed now...this must be better for the motors as well. LETS CALL IT PREVENTATIVE MAINTENANCE.
With the covers off like this, I wanted to see how the power mirrors behaved when cycled through the motions. ***make sure you re-engage the mirrors in the cogs...I placed them in the positions they were in when I started***
I pushed the button and both mirrors folded inwards. then I manually pushed both mirrors out and checked the indexing. I saw nothing out of the ordinary. Then I folded them back in where they were.
Both mirrors were tight from the hinge spring's tension...lets call this functional tension....and indexed properly.
Covers still off, I pushed the fold button again and both mirrors came out to their proper positions and stopped as they should...I was very surprised, to be honest. I was expecting to have to take the passenger side mirror apart all the way and see if I could figure this problem out!....
I did find that my mirror housing was not on correctly as I was taking it off...this mirror had been hit lightly before I got the car ( I could see the scrape under the mirror after I took the housing off)...It seemed to "float" past the correct index and go all the way forward. You guys probably can feel this too when you try to put the mirror in its proper position for driving.
One theory was that the housing was causing some kind of misalignment where the housing and base plate meet causing the mirror to miss its index. (Though it would find the other indexes when manually pushed closed or all the way open, or out of position....so Im not sure about this one...)
My other theory is that the car needed to find the correct index positions again and finally lined back up...I did cycle the power option quite a few times....the car also was trying to find the correct position every time the car was either turned on or turned off...as you all know!
At the very least, I have re-greased the mirrors and there is MUCH LESS friction in there...and its clean again...no grit or salt against the wires ect...
Now, this friction theory of mine may be off too...as the mirrors may never come out of these indexes unless the mirrors are pushed out of them...
either way, it may help one of you guys come closer to figuring this whole thing out....
"take it to the dealership" is an all too common phrase especially if you are out of warranty. Im convinced we can figure this stuff out if enough of us keep at it!
Last thought, if you are not hearing motor noises at all, and your mirrors are not moving...then you have a connection problem. The motors can burn out...but not from overuse, guys...only if there is a problem like low current, corroded connections, etc...Im convinced that if we check inside the housing once in a while, we could keep the corrosion and connection problem at bay...this in turn could help prolong the life of the motors......
just my long winded 2 cents.