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Rain sensor calibration?

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Old Nov 10th, 2018, 16:33   #11
MDS40
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an 'adjustable' auto sensor? what's that all about?

Exactly. Mine seem so hit and miss that i don't bother using them.
Rainx windscreen cleaner and intermittent wipe works fine for me.
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Old Nov 12th, 2018, 11:26   #12
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A pic of the sensor, I finally remembered to do it.
As Clan suspected, there is a bubble of air trapped there. Also I think the adhesive used is spots-silicone rather than a pad.
I have zero experience with fiddling with those - how do you get to it and correct it? (not even sure how to remove the plastic shroud, does it go out with mirror?).

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Old Nov 12th, 2018, 18:14   #13
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I tried removing the shroud once but stopped as it started screaming "try a bit more and I'll break off" so I left it.

I "think" it might just quarter-turn and release but don't take me up on that.
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Old Nov 14th, 2018, 13:54   #14
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To remove the plastic shroud, squeeze it front and back and pull it apart, and it should split in two.

The rain sensor is then held on with two metal clasps each end. Pull them out, and it pops off. Then just disconnect the wiring connector.

pics of my before, during and after fix:





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Old Nov 14th, 2018, 16:51   #15
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Quote:
Originally Posted by phutyle View Post
To remove the plastic shroud, squeeze it front and back and pull it apart, and it should split in two.

The rain sensor is then held on with two metal clasps each end. Pull them out, and it pops off. Then just disconnect the wiring connector. ...
uuu, nice, many thanks for this!!

so this weird pad is non-OEM solution? I see on 1st pic you also have a lot of small-round pads all around. Also - I thought sensor is the actual thing in the middle of this (that black part on windshield) where it is now covered with pad completely on your last photo. What part is the actual sensor "sensing" with??
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Old Nov 15th, 2018, 10:38   #16
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I was never able to find an OEM pad/kit, and this Rejel one is the only one I could find to fit the car. They seem to make pads for pretty much ever car. Maybe they are the OEM supplier, I don't know. But that pad setup is what the rain sensor should come with. I've seen people on forums posting that they've used clear silicone sealant instead, but I have no idea if the qualities of silicone sealant(refractive index, etc) are suitable for the sensor. This pad is, as the auto wipers now work 100%.

Edit: Actually, from some things I've read, it seems the pad isn't available as an OEM/Volvo part at all. The OEM solution is to replace the entire sensor if the pad is missing/defective.

The kit comes with a syringe of liquid gel, and the pad. You put the sensor on a flat surface, and slowly flood it with the gel, until it comes to the top of the lip (and making sure none goes into the hole on the left/passenger side). Tap it to release any bubbles, then leave it to set until it becomes tacky. Then you put the pad on, and refit.

I assume the 8 truncated disks are the sensors. They're arranged in a ring, and black material on the windscreen is absent over them to let light in to them. The black bit on the windscreen in the middle is just cosmetic to cover up the area that doesn't have sensors. I'm assuming the system works by sensing the light that is bent through raindrops, due to it having a different refractive index to the glass - which it why the material between the sensors and glass is important. If it has a refractive index that's similar to water, the sensors are going to think they're detecting a wet windscreen all the time. Or it's going to negatively affect the detection of actual water. This is why mine didn't work without the pad - the air gap between the sensors and the glass did not allow the sensors to take a proper reading of the light coming through the windscreen (and water if present).

There's also a small hole in the sensor on the passenger side (with a lip around it), with a corresponding hole in the black material on the windscreen. It doesn't get covered by the liquid gel, and the pad doesn't sit over it when seated properly. So it has an unobstructed light path through the windscreen. I assume it too is a sensor, maybe taking a reading that is then compared to the other sensor matrix. It's hard to see on your photo if it's covered in gel. It shouldn't be if it is.

Last edited by phutyle; Nov 15th, 2018 at 11:14.
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Old Nov 15th, 2018, 13:04   #17
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Quote:
Originally Posted by phutyle View Post
....
There's also a small hole in the sensor on the passenger side (with a lip around it), with a corresponding hole in the black material on the windscreen. It doesn't get covered by the liquid gel, and the pad doesn't sit over it when seated properly. So it has an unobstructed light path through the windscreen. I assume it too is a sensor, maybe taking a reading that is then compared to the other sensor matrix. It's hard to see on your photo if it's covered in gel. It shouldn't be if it is.
Heh, your explanation contradicts everything I thought about this sensor Never would think those 8 discs are sensors, especially if you are covering them with pad. That hole you refer to is not covered by gel, it looks like a small lens but in fact seem to be sensor as you mentioned.
Pretty complicated contraption, if you ask me, never thought much about this part but now I got interested, will research more about how it works.
will update if I get somewhere :P
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Old Nov 15th, 2018, 14:12   #18
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So a bit more reading shows that automotive rain sensors work by shining infrared light from inside the vehicle at 45 degrees to the windscreen. The measurement of the light that bounces back onto the sensors can determine whether there's water droplets over the sensor area via the phenomenon of Total Internal Reflection.

I'm now assuming the small hole with the lens that's not covered by the pad is the IR emitter. I think the black area in the middle of the sensor array actually assists in the IR light being redirected back to the sensors after initially reflecting off the glass. I still assume the refractive index of the pad is integral to the operation of the system, as the IR light has to pass through it.
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Old Feb 10th, 2020, 22:43   #19
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Hi
I have the opposite problem, on auto the wipers are over sensitive an will wipe once every couple of minutes even with a dry screen....windscreen is very clean. This only recently started, prior to that they performed very well indeed. Any ideas welcome.

2016 xc60 D5 awd + winter pack
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Old Feb 10th, 2020, 22:50   #20
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Quote:
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Hi
I have the opposite problem, on auto the wipers are over sensitive an will wipe once every couple of minutes even with a dry screen....windscreen is very clean. This only recently started, prior to that they performed very well indeed. Any ideas welcome.

2016 xc60 D5 awd + winter pack
Has the sensor ever been off for a new windscreen ? It must be stuck back on using the opaque white colour volvo pad , can you see any signs of it coming un-bonded?
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