afnakhai

After a year an half dealing with this faulty rain sensor and changing most of related components the dealer's mechanic thinks there is nothing else, I am finally told that it is not a problem.......go figure.
I have left my sensor setting on I all the time (rain or shine). When the out side temp. is above 70F and in the full sun the wipers come on intermittently.
The dealer has change the steering colum switch, boards under the hood and sepposedly the sensor itself behind the windshield. The only item not changed is the the wind shield itself.......which seems OK.
The dealer says there is nothing else to fix and I should live with it, turn it on intermittent when it rains.......nice service?
Please shine some light on this as to its technical reasons and or any other contributing factors? or am I completly wet about this subject?
It is really frustrating.
Frustrated C240 4Matic owner "05.

Gullwing

You shouldn't leave the sensor setting on all the time. Only turn it on when it might be needed.

Musikmann

I think you are completely wet, it is not faulty, and I'm surprised the dealer replaced all of those parts unless they wanted to make a few bucks from the MB warranty. Had they known that you leave it in the intermittant position all the time, they should have given up long before they did.

It is not designed to operate like the auto headlamp position; there are things hitting the windshield other than rain. Like Gullwing wrote, only turn them on when it is raining and like the dealer said, live with it.

whoover

I leave mine on year round. On both the C and S, they do not come on unless the windshield is wet when working properly.

My wife's C55 needed the sensor replaced twice before it stopped dry wiping. But it hasn't in over a year now that they fixed it right.

Tell them to fix it again.

mleskovar

I've read posts about some light and shadow patterns activating the wipers. Also, if you leave the wipers on automatic all the time don't you get a wipe action every time you start the car?

whoover

If the wipers activate on a dry window, regardless of the lighting there's a bad sensor. And no, I don't get a wipe action when I start the car. I think my 2001 S55 did that, but it also never once wiped in the dry exept for that start-up wipe. But neither 2006 car does that.

afnakhai

I agree totally. It is called "rain sensor" and it should come on when it senses rain and wetness on the window....when it is set on I.
I love my car and would have bought it regardless with or without rain sensor. I also love the this feature....kind of classy.
There has to be some technical explainations for this.

NY C32

There is no point of a rain sensing wipers if you have to manually turn it on/off when it may be needed.

Every one of my cars has had one since 2002 and I've left them on permanently, unless I was going through a car wash, and never had a problem

Fast55

+1. Both the SLK55 and my E55 are not the first MB's I've owned with this feature, and ALL have worked correctly. Even my new Tahoe has it and guess what? The wipers don't just "come on" when the windshield is dry. Your dealer obviously has no clue how to fix it. That doesn't mean it's not broken or that you should "live with it". Find another dealer and quit wasting your time.

afnakhai

Can you tell me what component was changed twice in your wife's car? Was it the sensor on the window? Thanks.

Gullwing

Driving 800 miles yesterday we encountered numerous rain storms. Got to the first storm and turned it to position 1, wipers came on when needed, but also would activate every so often when it was dry and sunny.

The sensor just looks at the light coming threw the windshield, it there is any change in the light it will activate.

whoover

That means your sensor is bad.

I have not switched mine to position 0, except for car washes, in two years. We had our first rain since April last week and when I pulled out of the garage the wipers came on for the first time since April.

A high rate of problems with the sensors have led to the urban myth that certain lighting conditions will activate a properly functioning rain sensor. When you have a good one, it works quite well.

sosh

Agreed, both my E Class and my ML500 work as advertised. I have never seen them come on with a dry windshield.

bfnnrgn

Well it doesn't actually sense rain. It's a light sensor. I've noticed that there's a turn near my house that if I go around it at a certain time of the day the light hits it just right and trips the wipers. It's kind of funny really.

whoover

It's a bank of infra-red light emitting diodes and IR receptors (which you can see by looking at the windshied area near the rear view mirror from outside the car). The IR is bounced at an angle through the windshield and will be reflected back into the sensors by the glass. If the glass is wet, the bounced image is blurred, and the sensors detect this as rain.

If the system is working properly, no pattern of visible light will spoof it. If it's triggered spuriously, the sensors are out of spec. It is very common. I guess they had a batch of bad ones.

mleskovar

A dirty windshield can alter the amount of IR reflected back to the sensor and trigger a wipe action. The system only works if all conditions are met and some of those conditions can be duplicated by things other than water.

afnakhai

I have given up with my dealer In Eugene Oregon. They do not have the band width to technically understand this issue....or it may be the service manager. I am going to take it to Salem OR or Portland dealerships to resolve. I agree it is optical and the sensor gets saturated when in direct sun (prestine windshield) for a period. I wish there was a way to get hold of the factory experts in Germany or the some service record for this issue.
Any help would be appriciated.
Ali

Moviela

The system is not sensitive to visible light at all. It is not sensitive to dirt or debris on the exterior of the glass, with the exception of droplet sized tree sap that is transparent. There are four infrared light emitting diodes, and four infrared sensitive photo-diodes in the assembly attached to the windshield. When the glass is dry, the light rays from the LED's travel through the glass to the inside of the exterior surface of the glass, and the light ray is reflected back toward the photo-diodes. The light striking the photo-diodes turns them on, and an electronics package informs the front SAM on the CAN-bus that the windshield is dry. When there is a rain droplet on the outside of the glass the light ray is bent at a different angle because water has a different angle of refraction than glass. This causes the light ray to head out from the windshield, and thus is not reflected back into the photo-diodes. The photo-diode turns off, and the electronics package informs the front SAM "Honey, I'm WET!" The front SAM knows what to do, slide some rubber over the wet spot.

Lets talk about what happens if the sensor is in direct sunshine. There is of course an Infrared component of sunshine, but most of it is reflected back by the exterior surface of the glass. That small amount that can get through, or human generated infrared from security cameras only turns the the photo-diodes ON! We already know that the electronics informs the front SAM that the glass is dry when the photo-diodes are on.

What causes the single wipe on a dry windshield at start up? Glitch, glitch, glitch. The voltage to the LED's drops slightly during the high current start up, and the light output dips a little. What happens when the photo-diodes are not illuminated? They turn off, and the front SAM gets the message to bring the rubber. The cure here is to change the windshield, unless out of warranty, a 20uf 20v tantalum capacitor across the voltage and ground on the glass connector will provide enough carry through current to keep the LED's from browning out.

If the wipers are turning on when the glass is bone dry, it is not from ambient light of any type, ultraviolet, visible, or infrared. It is not because there is a film of road dirt on the glass or if you have a tootsie roll in your pocket. It is because not enough light from the LED's is reaching the photo-diodes, and they turn off.

You can easily view the LEDs. Most camcorders have a "night shot" setting, most digital still cameras, and some cell phone cameras can "see" the infrared light from the LED's. They draw so little current, they are on all the time, so take your camera out at night, and you will see four little spots of light on your display screen. If one is off, or appears weak, you need to change the windshield. Have a helper start the car while observing the LED's, the LEDs should not blink or dim during cranking. To test each photo-diode, use an eyedropper to put a single drop of water on the LED's, one by one to verify the wipers start.

The LED and photo-diode assembly cannot be removed or replaced on the windshield with any more success than sending a fan letter to Hannah Montana will get you a date with Miley Cyrus. An OEM windshield should always be considered, because then the installer can't point to another party if the automatic wipers don't work.

I think the OP needs a new windshield.

whipplem104

It is true that it should not turn on except a change in the refraction in the glass. The early ones in the late 90's and the early 2000's would sometimes give false wipes when going in and out of a tunnel. When they switched to the new sensors that problem all but went away.
Most of the time the problem you are describing is due to the sensor not being stuck to the glass properly and having air bubbles in the sensor view.
Have you had the windshield repl. and was it factory glass?
Also when any piece of the system is replaced like the sensor, glass, overhead control panel. There are adaptations to perform. It learns the normal refraction in the glass. There is also adaptation for the color of the glass.
Many technicians do not know or do this.

Good luck.

Lee Wireless

See attached files

Lee Wireless

another attachment

Lee Wireless

Good luck