How does the rain sensing work ?
 

My "new" E320 has the rain sensing system and it is a love/hate relationship. There seems to be no rhyme or reason to how it works, and after it starts out wiping intermitantly, it usually just takes off and sweeps continuously. Is there any adjustment that can be made ?

I have no idea to the answer of your question, but I heard somebody tell me a story of taking their MB through an automated car wash (why????) and having the wipers kick on automatically - only to be destroyed by the car wash!


Ouch!

I find if it is barely drizlling on a cold morning, like this morning, the wipers will run continuously until the cabin air warms up. I think condensation forms on whatever the sensor is. After the interior warms up, they work as they should. I have two black thingies attached to my windshield in front of the rear view mirror. I am guessing one is the rain sensor. What's the other? 2001 E430

The other might be a light sensor for automatic headlights.

The rain sensor works by the principle of refraction (bending light???). Try sticking your finger into a bucket of water. See how your finger appears to bend? That's refraction, at least the way I understand it.

From your description, it sounds like the problem can be fixed by simply cleaning the outside of the glass in the area of the sensor.

If the wiper leaves even a light film, or streak of water in this area, the sensor will request another wipe. You can check this easily, by looking closely at the area of the windshield where the sensor is located, during a wipe. if you see any streaks, or if a slight film of moisture remains, clean this area thoroughly. I've everything from regular car wax to glass compound, with good success. Of course, make sure the wiper blade isn't the problem. Let us know how what happens.

That would be neat if I had automatic headlights. How would those be enabled? I better read my Owner's Manual book!

Both of these black thingies are about 2 to 3 inches square, with wires going up under the headliner.

The car does have built-in K40, but those sensors are on the front plate frame(laser), under the front bumper lip (radar), and behind the rear bumper (radar). I do not think the sensors in front of the rear view mirror stuck on the windshield re tied to the K40.

Have you searched? I thought I remembered seeing something about this a few years ago. Maybe a TSB? It probably wouldn't hurt to call the dealer and see what they recommend, unless it is "$500 plus parts"......

The optical sensor is located on the windshield at the rear view mirror.

Yes, the sensor has two parts. One LED, light emitting diode, and
a photo sensing diode, located some centimeters apart.

The LED sends light into the windscreen. When there no water on the windscreen, the light is reflected back and forth inside the screen, like in a optical fibre, and reaching the photosensor.

When water comes into contact with the screen, light "escapes", so less light is seen at the photosensor end. That means, that any water (or other contamination that will let the light "escape"), on either side! of the screen, can cause the wiper to wipe.

I think they have some kind of material on the inside, to reflect light, but it will not hurt to clean the inside as well?

Do also remember, that the sensor must be fastened correctly to the inside, or else, the amount of light, going into the screen, and escaping a few centimeters away, will be insufficient to declare the screen as clean:-)

br,
syljua