rain sensor after windscreen replacement

[sathound]

Has anyone else had problems with the rqain sensor after windscreen replacement. It now seems to lack sensitivity. From the outside it appears as if there is an air gap between sensor and screen and removing the module it appears that the silicone rubber surface of the sensor is very uneven.

Does anyone know if the gasket requires replacement?

[Crasher]

They are very fussy about how they are stuck back on, it doesn’t sound like it has been done properly.

[sathound]

They are very fussy about how they are stuck back on, it doesn’t sound like it has been done properly.

It doesn't appear that they have used any adhesive. The sensor has simply been pushed back into the rectangular rubber boot and is held in place by the mirror sliding on beneath it. The surface of the sensor appears to be a translucent rubberised silicon but the surface is very uneven.

Does anyone have any knowledge of what the correct fitting procedure is?

[Crasher]

PM me your email address and I will mail it over.

[snapdragon]

Yes, I had the same problem with Autoglass. They has to order a new Gel Pack from VW, and came out and fitted it a few days later. I think it's some sort of IR filter. Mine also looked different from the outside instead of black, it looked clear and wrinkly.

[sathound]

Just to conclude this thread for the benefit of others that may search on this topic in future:-

I had the winscreen fitters back today. They had attempted to reuse the original adhesive gel filter pad fitted to the rain sensor (they apparently cost about £40 so there is an incentive for them to do that) but in the process of removal and refitting this had become distorted with an uneven surface and consequently would not make good contact with the screen. Consequently there was an air gap between sensor and screen and from the outside the sensor area looked clear and wrinkly as snapdragon said, not black like new. The old pad was removed with a razor blade and a new one fitted and hey presto, the sensor looks much more black from the outside of the car and the rain sensor responds to liquid on the screen whereas before it didn't intermittently wipe even on the highest sensitivity even in moderate rainfall.

Thanks to all for your help

[claranet]

The Rain sensor uses an array of infra red LEDs and a infra red sensor.

The Infra red LEDs shines a beam of infra red light onto the inside of the outside surface of the windscreen; the infra red beams are reflected back and depending on how many water droplets fall in the area concerned the ECU behind the dashboard somewhere, calculates the requirement and controls the wiper accordingly. I would guess that either the windscreen is of a different thickness to the original or the sensor had not been attached properly possibly with air bubbles trapped in it somewhere.

I would have thought that your VW dealer would have the test software to re - calibrate the system.

This is how my Tyre pressure warning light problem was cured.

Regards claranet

I hope this helps.

[sathound]

Claranet,

This was not a case of re-calibration but simply that the optical interface from the sensor to the screen needs to be good and removing the sensor from the old screen and replacing it on the new screen without replacement of the relevant gel filter material renders them useless unless you are very lucky.

I would have thought that a replacement screen with the mirror mounting already fitted specifically for rain sensors might have come with a replacement gel adhesive but apparently not....so beware if you have your windscreen replaced by a 3rd part windscreen company and ensure that the rain-sensor is refitted correctly at the time and ask for a test by spraying liquid over the area around the rear-view mirror.