My wipers are starting to come on when its not raining. It used to happen once in a blue moon, but now its becoming more frequent.

I dont think this is related, but it started happening around the time the wiper fluid refill message came up.

Its not a big deal because I can turn it off, but maybe there is a quick way to reset?

 

I have the same problem just have to learn to live with it.

 

I'd like to know if there is perhaps a reset for this or maybe just wait until next vehicle service to have it reset.

 

I have a dim memory of reading that someone mentioned being able to re-calibrate the rain senors through STAR. I can't find where I read it, but I want to say that someone mentioned being able to do it with aged/sand-pitted windshields, etc. If you can, that might solve the issue.

Maybe someone who has STAR can play with it and let us know?

 

The system relies on the refractive index difference between the glass and the glass with a drop of rain on it. When the windshield (windscreen for our friends down under) is clean and dry light from four LED's reflects off the outside layer of the glass and falls on four photodiodes that report the relative "brightness" to the front CAN. If the light is bright, the wipers stay off. If there is a water droplet on the glass, the light beam does not reflect, rather is bent and shoots off into space. This results in less light on the photodiodes and the front SAM thinks "time to wipe."

Factors to consider. LED's have a finite life. The light is not visible to the naked eye, but you can see if they are all on if you point any electronic camera at them, cell phone, video camera, or digital camera. If one or more are out, you need to replace the windscreen because in the workshop it is almost impossible to attach the assembly to the glass properly. The assembly might have delaminated from the glass, and this requires a replacement.

There is a sensitivity adjustment through STAR diagnostics because the sensitivity of the photodiodes varies over a wide range.

It is possible that car care products are causing undesired operation. Any thin film coating on the glass can cause the infrared light to be refracted into space. Products that are emulsion based, or containing silicone can cause this. There are solvents that can remove most anything, but the easiest way is to use an abrasive cleaner that will not harm the glass. Bon-Ami is the choice of most professionals to really clean the glass. It is a kitchen sink cleanser, a white powder but different from most because the polishing agent is egg shells and will not scratch the glass. (Don't use other kitchen cleansers, they will muff the glass.) You don't need to clean the entire glass surface, just around the sensors. If you have streaking or skipping of the wipers, Bon-Ami will fix it too.

 

That's a very good explenation Moviela, perhaps that is what is happening to my car. The LED may be getting a bit old. I cleaned it and it still 'wipes' sometime.

Could the heat be causing it? Here in Australia have have had very hot days recently and it so happens that it this started when the summer hit.

 

Moviela,
Thanks for the good write up. Carsy.

 

When's the last time you changed your wipers? Mine was very erratic and I changed my blades and it made s big difference. Works the way it should again.

 

A slight possibility. Heat causes the output voltage of the photodiode to go down as the temperature rises. At 0C the output is about 500mV, but it only drops to 360mV at 40C. Most circuit designers compensate for ambient temperature changes, so I doubt it is the cause. An increase in the Ir from sunlight would cause the output of the photodiode to go up, and that would serve to keep the wipers off.

If you can find someone with STAR diagnostics you might try an adjustment of the sensitivity.

 

Or you could strip the glass of whatever contaminants are on it. Try cleaning it as much as you possibly can and go from there.

 

From what has been said about how the sensor system works I assume that products such as rain-x should definitely not be used. Even though I use it on our other cars and love it I have never used it on my 280 due to my concerns that it would affect the rain sensors. Several years ago I had a stone chip repaired on my other car and the repair guy asked, after several attempts to get the repair stuff to stick; do you use rain-x? I told him yes and he said, well the repair will not last, you will eventually have to have the windshield replaced. He said they have never been able to totally clean the rain-x from the glass enough for the repair material to bond. He was right, the repair didn’t last a month. If anyone uses rain-x and it does not affect the sensors let me know, I don’t want to be the guinea pig, I’m sure a new windshield with sensors is not cheap.

 

I use Rain-x on my 204 & have no problems at all. Also had a chip repaired & its still there.

Rain-x allows me to drive at highway speeds without the wipers on. Saves on fuel because the pads are not feathering the discs .

I wish I could cancel this feature as it not req in warm climates..

 

Newer screens with embedded sensors give less trouble. The system can be recalibrated with Star. As Movie says clean the sensor area of the screen of silicon or mineral deposits with an abrasive metal polish or similar - in SA we use Coke for it's phosphoric acid content. Diet Coke being best so it does not goo things up. Movie used to advocate using a polish made of egg shells.

 

^ +1 for using Bon Ami as a safe and effective glass cleaner.

BMW issued a bulletin in the ‘90s (#61 02 94 3990) recommending its use to cure chattering wipers owing to windscreen contaminates.
My stash of GM’s PN 1050011 “Windshield Cleaner Powder” is actually cleverly repackaged Bon Ami.

No clue if it’ll solve anonymousmoose’s rain sensor woes, though Faultless’ blend is an oft-proven consumable around most every workshop and household.

http://www.bonami.com/index.php/prod...wder_cleanser/

 

Wish it was available in SA. I don't think I saw it on the shelves when I lived in Aus. But I think Anon get's the idea.

 

So clean the windows with diet coke? Hmm. seems counterintuitive but mine act up, too and the wipers chatter a little.

 

It used to be... haven't seen it lately.

Used it once on a hot brass cane steam train wheel bearing to give it a little more clearance !! With success!!

 

Do you guys leave your wipers set to "auto" at all times? I haven't had this happen on my car and I'm pretty glad.

Cleaning with Coke sounds pretty interesting. Makes you think twice about drinking the stuff.

 

The phosphoric acid in Coke strips off silicone & mineral scale from a windscreen.
Obviously you wash with water after that. Movie was worried about goo'ing things up with US Coke because it contains corn syrup & not cane sugar. Very old discussion we had.

 

Works great for getting bugs off the windshield also. Seen this done on patrol cars many times.

 

So I learned something new today and am glad I stopped drinking coke 14years ago

 

Phil my car will wipe randomly with them set to auto and it not raining. Once it starts raining I turn the rain sensor on but it's off at all other times.

 

Keep the windshield spotlessly clean as others have pointed out, and the rain sensor works wonderfully. I use Bon Ami on a regular basis to clean the windshield, and I leave my wipers set to Auto all the time, and they work flawlessly. Never have random wipes, or other issues. But, I am ****, and wash my car and windshield weekly

 

If that makes you think twice about drinking the stuff, you should see what Coke/Pepsi/Dr. Pepper (or any other dark soda for that matter) does to concrete. Hint, it eats right through it. I worked at PBG in Denver many years ago, and stopped drinking soda after seeing what the syrup does to concrete.

 

If your complaining about the wipers going off randomly when set to "auto" or the sensor then you need to be smarter then the car, the system isnt supposed to be left on all the time. If you complained about that at an MB dealer they would tell you to turn your wipers off when its not raining, and put it on auto when it was.