Rain sensing wiper

[NickD]

I have recently, this Monday, has the windscreen replaced on my 2010 car. It has rain sensing wipers. They worked before the screen was replaced but the technician could not get them to work afterwards. He had replaced the silicone pad and used a gel between them.
At that time he stated that the sensor works by sensing the vibrations of the rain hitting the windscreen rather than optically and that the lense was purely for the light sensitive lights!!!
He then called a colleague and it was left that the first guy could not fix it, the guy he called said that Renault can take up to a week to calibrate and I called the office to request someone else look at it!!!
So this morning a second guy turns up, has a fiddle gets them to work after a fashion by squirting quite an amount of water on the screen in the sensor area. Again, it is obviously not going to work, but it is left again as give them a try.
This afternoon it rained and as expected, nothing. So I had preempted this with another call and had a 3rd and 4th guy out this afternoon to look at it again. This time he replaced the silicone pad with a two pack gel and it did seem better although it has not rained since to check. However even drenching the screen only gets the wipers to wipe about every second, so they briefly park, and while they do wipe now if the lense area is wet it still does not seem right.
The first thing that stood out was all of their insistence that the sensor unit operates by "feeling" the raid hit the glass and a couple of them even tried to get it to work by tapping the screen. Now this seems lunacy to me to even suggest it on so many levels from road vibrations to playing the radio but mainly from the fact these things work on the refractive index of the glass. However as I think all 4 said "they work on the pressure of the rain" am I being stupid?
Secondly and more importantly do these things need calibrating? There is the resolution setting on the column stalk but that seems to do nothing.
Does anyone know if it is the sensor it's self that is the issue, the controller elsewhere or something else?

 

[turkie172]

I retro fitted the rain sensor after getting the windscreen replaced just asked for the different window type and got the roof loom etc. from another car. Now the connector into the rain sensor is nearly in my view impossible to disconnect in a normal fashion check for damage I bought the gel pad from eBay ALEXCOP but the performance of the sensor can be all over the place if the windscreen tends to smear and streak make sure no bubbles in the gel and on my type the oval centre has no gel I assume that is the light sensor for the auto headlights. I've put everything I can find on it now you cant say you don't know you will have to say you don't have a clue. Remember the stalk needs to be in the second position to arm the auto wipers and the twist ring adjusts the sensitivity the only other thing can be the wiper mechanism it the wipers are flaky there is a cut out function to avoid damage if the mechanical resistance is high and the joints need lube. Good luck

https://www.ebay.co.uk/itm/RENAULT-...f:g:CWQAAMXQEgpTEwf7:rk:1:pf:1&frcectupt=true

 

[NickD]

Thank you.
I had seen the 85A removal and refitting of the sensor but not gone deep enough to see about the CAN bus connection to the UCH which is basically the very last part, just above this post. It is quite possible that the wiper stalk sensitivity settings are also not working correctly, but the fact that the wipers always park for at least a second would suggest that there is a control issue rather than a sensing issue.
Prior to the screen replacement I believe the wipers would lock into continuous wiping on early morning starts where the screen repeatedly has condensation on the outside when cold until it warms. However I don't recall rain ever setting them fully into continuous so I could be mistaken. It would seen that some diagnostics of the UCH actions are required first.
As far as the sensor goes, it is my understanding that these work by refraction. If you remember your science from school or even the front of Dark Side of the Moon, light is bent or refracted as it passes between different density materials, so inthis instance air and glass. So the sensor has a light source, an LED and the lense in the unit focuses that at the screen. Some of that is internally reflected at the boundary of the glass to air, just like relections in a puddle, and is received back by a separate sensor, which I assume is also linked to the lense. Water droplets or just water in general on the screen changes the refractive properties at that glass air boundary and some of that light is transmitted or refracts in different directions and so not as much comes back to the light sensor and so gives a signal to the UCH to act on. In writing this it has therefore occurred to me that since there has to be an angle between the light source and the receiver, which will be created in the lense, that the distance and position away from the glass must be critical to get the angle correct which means the thickness of the gel pad or the correct mounting of the actual sensor mounting which comes attached to the windscreen will play a part in this. If the mounting is not square or for some other reason not to spec or that the gel pad is thicker or thinner than it should be this would likely cause a sensitivity issue. It would however be a wise software engineer that realised this and that the UCH is programmed to look at average light levels over a period and only react to sudden changes and so does calibrate to average received light from the senor over time rather than just an absolute level.
In addition I would suspect the same lense is used (it is faceted) to look at light levels for the auto lights as there would appear no other aperture for doing this. I have had one of these units to pieces and all the other lense looking moulded parts as shown in 4 above are all opaque, moulded in the body plastic of the base unit and so they are to reflect light internally to an array of sensors. I would love to know how they actually functioned.