W211 Rain Sensing Wiper Problem

[DieselE]

I have two annoying problems with my car (the other one is posted in the electronics section). The problem for this section is when my rain sensing wipers are turned on, they detect the start of rain. As the rain gets heavier, they speed up slightly but no longer speed up to normal wipe or double speed wiping.

My local dealer said that nothing was showing on the Star Diagnostics and they could not find a fault. I then said that was totally unsatisfactory and I would by writing to MB at Milton Keynes. Surprise, surprise but by the time I picked the car up they had decided to order a new rain sensor.

Main reason for the post is to ask if anyone has experienced a similar fault and what was the solution.

 

[Dryce]

Main reason for the post is to ask if anyone has experienced a similar fault and what was the solution.

I have recently had a Ford and Vauxhall with auto wipers along with my W211. All three are (let's be kind) 'idiosycratic'.

One consistent behaviour I've noticed between all three is that dense small droplets (heavy drizzle?) causes faster wiping than is wanted. Some patterns of heavy rain appear to confuse the system so that it slows down or if working intermittently doesn't speed up.

Where they seem to work best is in intermittent rain or when you get sprayed passing a truck. The rest of the time they're 50:50.

The technology is imperfect.

 

[Flash]

Peter: Sounds like a faulty sensor (which is integrated into the black mounted box on top of the windscreen). A replacement should fix the issue. Also, the sensitivity of the rain sensing wipers can be adjusted by the Stealers in addition to the sensitivity of the auto lights.

One of my W203s had an issue with the headlamp locators (these function when it is dark and the exterior lights activate when unlocking/locking the vehicle for a period of time. I told the Stealer from the start that it was in my opinion a faulty sensor (black mounted box on the windscreen) BUT they did not listen and instead spent 7 HRS under MB warranty/labour at looking at the wiring of the vehilce etc.... In the process they disturbed the auto sensing rain wipers too and returned the vehicle back saying all was fine when it was not and the rain sensing wipers were not functioning and vehicle was returned back worse off than before. After consulting with Tech Support they were instructed to replace the black mounted sensor box on the windscreen and all was fine...!

Don’t worry all should be fine when they have replaced the sensor box and re-programmed the rain sensing wipers via STAR. Do NOT let them take the vehilc apart to look at the wiring etc.!

 

[ddentrec]

Had a similar problem on my W203: light rain was OK. But if the screen got sprayed by a passing truck then the wipers would not wipe for about 2 seconds: underpant-filling on a dark night I can tell you. Conversely on summer days the wipers would sometimes wipe themselves.

Dealer said that this was 'a characteristic'. I said it was a potential safety issue. Anyhow, sensor was replaced under warranty - is better but still not foolproof.

Also, the sensor sensitivity can only be modified by the dealer.

In my experience the best rain sensors are VW: sensitivity can be set by the user and it is super accurate: my Golf had them and they were so good I never fiddled with them in 4 years I owned the car.

 

[Flash]

Dealer said that this was 'a characteristic'. I said it was a potential safety issue. Anyhow, sensor was replaced under warranty - is better but still not foolproof.

Sensitivity/setting of the rain sensing wipers on all my previous cars and the current one is fine. Its not a characteristic at all!

Sounds to me as if your sensitivity of the rain sensing wipers could do with a little bit of tweaking and Stealer is just being lazy.