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2003 E500 Sport
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I've got a new one for ya. I keep my wipers set to "auto" mode so they come on when it starts raining. For the past two days, they will come on at random times and do a single pass. I drive about 10 miles to work, and they will activate about 3 times per trip. Is there a sensor that might have something on it that I need to clean off? Any help is greatly appreciated.
 

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2007 E550 4Matic P2,Pano,Voice,Park,Trunk,Fold Seats, Black/Ash;;; 1989 560SL (sold 11/1/10)
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Mine acts crazy at times unless there is logic to it. In light rain or mist it goes too often and too fast. In ice it doesn't know what to do. But weirder than that on most days as soon as I pull into the garage the wipers swipe a single pass though its totally dry.

I would love to know where the sensors are and what makes it tick.
 

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222.132 & 221.122 & 213.050 & 906.633
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The sensor is at the top midle of the windscreen. Keep it clean and use good wiper blades, should work ok then.
 

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2006 E320 CDI
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My understanding is that these systems work by detecting light refracted through water (not by detecting moisture, as one might suspect). You may have some contaminant on the glass that is tricking the sensor into thinking that there is water on it. As Diesel Benz says, keep the glass over the sensor clean. Also, the system will not work effectively if your wipers are worn and leave streaks.
 

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HFMB said:
My understanding is that these systems work by detecting light refracted through water (not by detecting moisture, as one might suspect). You may have some contaminant on the glass that is tricking the sensor into thinking that there is water on it. As Diesel Benz says, keep the glass over the sensor clean. Also, the system will not work effectively if your wipers are worn and leave streaks.
That's why (at least in the W163) manual, it says to leave the wipers OFF when it's dry.

Does it say that in the W211 manual? And yes, HFMB, that's correct.
 

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Diesel Benz said:
The sensor is at the top midle of the windscreen. Keep it clean and use good wiper blades, should work ok then.
Too be more exact the sensors are built in to the back of the rearview mirror.

As for these things tripping irregularly, I have had it a couple of times, seems scattered shade/sun emitted through trees sets mine off as we have lot of old big over hanging trees along some parts of south Jakarta's roads and when that SE Asia sun get's fired up it sets it off but maybe 5 times since I have had the car the last 7 months. As well keeping the area clean where the sensors are helps as well. Other than that mine does not give me of a problem and I leave them on auto all the time.
 

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"My understanding is that these systems work by detecting light refracted through water (not by detecting moisture, as one might suspect)."

Uh...Ok...But what happens when you drive in the rain AT NIGHT???
 

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06 Corvette, Harley Davidson, 08 E350 Sport
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Don’t have my new E350 yet but the ’06 DTS I had, the manual
said to leave them in auto, and it is NORMAL that they will swipe
every once in a while even when no rain.

I never liked that as I “cringed” every time they went across my
windshield DRY. So I left them off until it rained and then turned
them on auto.

By the way I never asked, will my new 08 E350 have auto wiper
sensors?

jimm

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Arriving U.S. tomorrow: 08 E350 Sport, P2, Black/black,
Parktronic, Voice, Bluetooth, Burl Walnut, Split rear seat,
Rear mud flaps
 

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Jakarta Expat said:
Too be more exact the sensors are built in to the back of the rearview mirror.

As for these things tripping irregularly, I have had it a couple of times, seems scattered shade/sun emitted through trees sets mine off as we have lot of old big over hanging trees along some parts of south Jakarta's roads and when that SE Asia sun get's fired up it sets it off but maybe 5 times since I have had the car the last 7 months. As well keeping the area clean where the sensors are helps as well. Other than that mine does not give me of a problem and I leave them on auto all the time.
I was not accurate but this one could be misunderstood too. The sensor is attached directly to the windshield, the device is not part of the rear view mirror but it is under the cover, on top of the windshield, behind the rear view mirror (which Jakart Expat must have meant).

As previously explained, the sensor emits light (IR) and detects the reflected light from water or rain drops on the glass (opposite side of the glass).

I have not seen wipers come on on their own. I would guess the reason still being dirt or something similar on the glass, if light conditions (IR specifically) change and there is some dirt, the detector may interpret new rain drops appearing on the glass.

I consider it a safety issue to leave the wipers on, at least at certain conditions. The point being that even if it is not raining, you may get splashed from a pool of water, by some fellow driver and get blinded by a lot of water. The auto wipers react a lot faster than the driver itself.

An -08 E must have auto wipers, I assume it is standard on all MB cars, likely including A-class.

The W221 has two sensitivity levels. I don't think that is really necessary. I remember a BMW (5-series) having auto wipers with a non-discrete sensitivity setting, not bad but not really necessary either. I still consider a clean glass and good wiper blades all that is needed, unless of course the control unit or the sensor is broken.
 

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I have had similar problems with my wipers. Now I know that I am not alone. After reading this thread, I feel more enlightened.
Nice thread! Got to thank you all!
 

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Okay, so, people. Leave them off when it isn't raining, and turn them on whatever setting you so desire when it is raining. Doesn't sound too hard to me...

And if the wipers do in fact wipe on a dry surface, it wears them down/puts tiny knicks in the wiper blade, thus hampering the ability of the wipers to keep the road visible in, oh, say the next rain storm you have.
 

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themantm said:
Okay, so, people. Leave them off when it isn't raining, and turn them on whatever setting you so desire when it is raining. Doesn't sound too hard to me...

And if the wipers do in fact wipe on a dry surface, it wears them down/puts tiny knicks in the wiper blade, thus hampering the ability of the wipers to keep the road visible in, oh, say the next rain storm you have.
And could possibly scratch the glass if a little rock gets caught underneath the blade!
 
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