E430 Auto dimming mirror oddity

[Veridian]

Folks,
I dont know if any of you have come across this, if so any ideas on the remedy - me thinks perhaps swapping over a couple of cables.. anyway, my W210 has an auto dim mirror which worked fine, until I knocked it - d'oh - whilst reaching to get something of the dash in a hurry - about two months ago. Anyway, now the nigths are drawing in I noticed the auto dim function isnt working.. or is it....
On close inspection I find that when I turn the key to position 1, - cover up the front facing light sensor, and shine a light on the mirror face/wait for a car with lights on to pass from behind, the mirror dims just fine, but as soon as I start the engine it reverts to the usual 'daytime' state!.. Any ideas on how to rectify this, since not much good having an auto dim mirror that only works when youre not moving Many thanks Steve

 

[Birdman]

Try sticking something over the sensor device when driving in the dark to see if the mirror then dims correctly. Btw do you have a rain sensor?

 

[Veridian]

Rain & Mirror

Hi Birdman, yes I do, but its never actually worked, (though sometimes on journeys where ive had the wipers on for an hour or so, it will work give me intermittent wipe at a constant speed). As a work around for the mirror, I took it apart and put a voltmeter across it to see how/where the power was flowing, and I found that as soon as the ignition was 'started', power flowed through one of the points - cant remember which one - and that stopped the mirror from working - so I simply took out that pin from the plug and now the mirror works fine.

 

[Birdman]

Bizarre.
Auto dim works only when the road lights are switched on so I take it they were! You think the knock created a short across the faulty pin?
The rain sensor requires a clean windscreen and an efficient wiper blade. Anything less and it's simply a damned nuisance. Plus, I miss the old 'intermittant' setting, as the windscreen gets too watery waiting for that 'occasional' wipe.
Technology - who needs it...

 

[Veridian]

Hi Birdman , having done a bit of research on similar posts it turns out I have a replacement - non MB windscreen - its a Splintex, Im wondering whether thats whats causing the problems. Malcolm indicates its a pretty common cause of duff sensors - or rather sensors being unable to see out. So if I want auto wipers its 'Hammer time'! I took the sensor off and once it can 'see' the screen it seemed to work. As you say .. its too clever by half! Talking of sensors, from my tax disc holder I notice there is a cable dropping down and into the dash. any idea what its for.. is it a radio receiver for the central locking.. just wondering? Thanks

 

[Birdman]

Talking of sensors, from my tax disc holder I notice there is a cable dropping down and into the dash. any idea what its for.. is it a radio receiver for the central locking.. just wondering? Thanks

You're saying there's a cable (not an aeriel) attached to your tax disc holder? Weird. can't have any relevance to anything Mercedes designed. Maybe used for some attachment introduced by a previous owner. Beats me!