Auto dimming rear view mirrors

[Midhurstman]

This will probably have dozens of you replying with "tell me something new, this has been discussed to death." Well I have looked through as many old posts as I could and, although much is covered, I could not find all the info.

My zed had this option fitted at the factory, for internal rear view mirror and both door mirrors. After buying the car (9 months ago) I knew it wasn't functioning correctly but lived with it. several of the posts I read mentioned a website, http://www.mirrorjohn.com, this is well worth a read for those who have not seen it. From this I discovered that the dimming option on mine has failed, probably due to the inferior fluid (BMW changed supplier in 2007), leaving all of the mirrors permanently dimmed. lots of old posts I read say things like 'nothing seems to change on mine' or 'this option is crap and does nothing'. I wonder how many are driving around like I did with the system failed to permanently dimmed glass? Not so bad during the day but a definite safety hazard at night.

Buying new replacements from the dealers is so expensive it's out of the question. The good news is that I purchased the new improved replacement glass from mirror John (£99) for the internal rear view and it's now working perfectly. The bad news is that both door glasses have the same problem and also need replacing, at £150 the pair (used oem from John)

Some of things I have learned whilst looking at this, is that some vehicles have the auto function on just the internal glass(mirror)- you can tell on the door glass by a black plastic surround on the glass, which I have read is only fitted on auto dim door mirrors, not on standard non auto. The release lever for the door mirror glass is at the top of the glass, not the bottom, as with many other BMW models, and, I am ashamed to admit that I did not know this, that the sensor on the back of the internal mirror housing (which looks at the front of the car) is only to determine when twilight (or very dark conditions) occurs. This then leads to the sensor on the front of the plastic housing (looking at you) activating the dimming operation when a light source (headlights of the idiot who has just cruised up to 4ft from your rear bumper) falls on it. The auto dimming therefore can be checked easily during daylight by putting a finger over the sensor on the back of the internal mirror plastic housing, simulating darkness and causing the daylight on the front sensor to immediately dim the glass. If it doesn't, you have the same problem as me. It would also be a good idea to check that fuse 25 (5A) that protects this system is not blown (who's gonna be that lucky!). Finally, if only your internal mirror has failed, the door mirrors should remain bright and not dimmed, as the fluid sandwiched between the 2 layers is activated by the internal mirror sensors. As mentioned, if they are also permanently dimmed and the internal mirror is repaired and now working correctly, which proves the sensors are working,(as with mine), they have also failed and need replacing.

[x-driver]

A different question I'll just post here as the topic title fits.

Does anyone have a problem with auto dimming mirrors that when you drive with your top down when the daylight is fading but you can still more than clearly see around, your headlights (if automatic) will already turn on and the mirrors will dim probably just because the daylight from behind bothers them. If you cover the light sensor on top of rear view mirror, the mirrors will lighten up.

Is it the way it is or can it be somehow solved, adjusted, anything?

[TriggerFish]

I have had this in other hardtop BMWs (and other non BMWs, too) when the sun is behind you

It's just working off a differential of light behind and in front. If there's more light behind (like a setting sun), the mirror will dim. No software options to tweak this in the e85/6.

[x-driver]

Well there wasn't any sun visible at all when I last observed the mirror behaviour. And the sky was partly blocked with trees all around. There are 2 other BMWs with auto dim mirrors at home but I never noticed any unwanted behaviour with them.