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      08-11-2018, 10:47 AM   #1
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DIY: Repair side view mirror glass motor assembly. Side view mirror erratic behavior.

Hi all,

I repaired my side view mirror glass motor assembly as part of another DIY to retrofit folding mirrors. As with any of my posts, please do it at your risk. You don't have to remove the whole mirror assembly and it can stay in the car. This DIY can be used for problems arising due to:

1) Corroded electric contacts.
2) Stuck motor gear and movement mechanism
3) Burnt or stuck motor
4) Broken gear and movement mechanism (if super glue can fix it)

The typical symptoms are:

1) Mirror glass moves up/down but not left right (and vice versa). You will see that if you switch only the mirror motor assembly to the other mirror, the up/down problem becomes a left/right problem indicating that one motor might have failed. This was what happened in my case.
2) Mirror glass doesn't move at all
3) Mirror glass movement is erratic and for cars with memory function, the mirrors doesn't seem to store the set position.

First, remove the mirror glass. Move the mirror glass towards the car by hand. Then use a trim tool to gently pry around the edges slowly starting from the outer most edge. Disconnect the two wire plugs and keep the mirror somewhere safe. There are many DIY's for this on youtube and bmw forums.

Please also watch this DIY:
and although it's not for e90, its very similar and the video helped me a lot. Once the glass is removed you can see the mirror motor assembly with a screw at the center. Remove the screw and gently wiggle the assembly to take it out. See attached pictures. I recommend doing the rest on a work bench.

Pull the plastic cap gently from the three clips/tabs on the electrical contacts side. Clean the contacts with a fine sandpaper/file and later using an electrical contact cleaner. This may fix the erratic behavior problem. Clean also the female plug contacts on the mirror assembly. Put the mirror motor back in the mirror assembly and test it. Continue with the DIY if this doesn't solve the problem.

There are two motors in the mechanism. One for up/down motion and one for left/right mechanism. There is an 8 pin contact plug on one side. Two for 12V supply to one motor, two for 12V to other motor and four pins for what looks like a sensor mechanism to detect start/stop positions for each motor. Test each motor using a 12V DC supply. For each motor, reverse the polarity and see if they move in both directions. Be careful not to short circuit your power supply as the pins are very close to each other. If it's confirmed that one or both motors do not move, we open the mechanism.

There is a plastic lock, secured with two tabs at the end and two clips on the side. Use a small screw driver to pry it out. Be patient, it can take some time to do it without breaking the clips/tabs. Then rotate the outer ring clockwise to unlock. Remove the 10 clips that secures the cover to the motor housing. It's a bit tricky and can take time. A tip is to remove one clip and peg something near it, while moving to the next clip. One the cover is removed, you'll see the two motors and gear mechanism. For me one of the motor shaft seemed stuck. I took the motor out loosened the motor casing clip a bit with a small screw driver, applied some force to the motor shaft and it worked. The motor looks like a standard 12V motor used in toys so you might try your luck to find a replacement in a hobby/electronic store. Sometimes the gears might be stuck so applying some lithium grease can solve the problem. If the gear mechanism is broken super glue may be a solution depending on the extent of damage.

Assemble the motor mechanism back and test with a 12V supply to see if it works.
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