Volvo rain sensor--works in the shop, not in the field

I’m posting this question here in some desperation. I had a new windshield installed on my 2004 Volvo XC70 because the old one was cracked. The insurance paid for what it called an equivalent windshield but did not pay for an original equipment windshield. Since the installation the windshield wipers do not work as they should when I set them on the rain sensing mode. The wipers may make one or two sweeps on occasion, but generally they just sit there. The problem is that both the glass company and my Volvo dealer have tested the sensor and it works just fine–that is, if you spray water on the sensor the wipers respond as they should. There are no codes or other indications of trouble. The only problem is that the sensor (or something) doesn’t work when the car is actually in the rain–as I said, at best I get a sweep or two and that’s it. Before the new windshield I had no problems. The professionals are stumped. Does anyone here have any ideas?

Either the new windshield is effecting the rain sensor, or it was damaged during the installation of the new windshield.

This sensor is located in front of the rear view mirror mount facing out the windshield. And here’s what it says when dealing with this sensor. WARNING: The silicone surface of the sensor must not be touched. Any kind of dirt or contamination on the surface of the sensor will prevent it’s use.


It probably is the windshield itself or the sensor installation. Here’s a description of how the system works. I’m inclined to agree with Tester’s theory on the surface of the sensor having perhaps been handled…

Thanks for the thoughts, but they don’t get at my problem. My Volvo dealer has looked at the car and determined that the sensor is working properly–in simple terms, when you spray water on the windshield the wipers activate. In addition the computer program is set at maximum sensitivity and the electrical connections seem to be OK. The problem is that when I take the car out of the shop and onto the road the wipers no longer act as they previously did. When rain is light to moderate they will at most give one or two sweeps. When rain is heavy they will sweep, but less often than they should so that their usefulness is limited. In any case, when the rain is that heavy the normal speed settings are adequate and the rain sensing is not necessary. What no one (including me) understands is why the wipers test out OK in the shop but do not work in the field. That is where I could use help. This happened when I had a non-Volvo but supposedly equivalent windshield installed (my insurance would not pay for a Volvo windshield).

Is the problem only during the day, during the night, or both?

It’s all the time, day and night, city and country.

Have you tried very lightly sanding the outside of the windshield where the sensor is?

Have you considered just abandoning the entire issue and simply turning on the wipers when you need them? I mean, that’s what the rest of us do without suffering any undo physical effort…

Not all of us. It’s a handy feature to have in light rain, especially in one of the rainiest cities in the US.

Every once in a while Caddyman nails one.

Reminds me of the old saying “He’s so stupid he doesn’t have sense enough to come in out of the rain”.

Thanks man.

There are a couple possibilities that come to mind. The most probable to me is that they did not exercise the proper care in re-installing the sensor when they replaced the windshield. The technology relies on ATR measurement of the emitted infrared light bouncing off the EXTERIOR surface of the windshield. If the sensor is not perfectly flat against the interior surface of the windshield, it will lack the necessary sensitivity and may even be fooled by reflections from the interior surface rather than coupling into the glass properly.

I was also curious if automakers were using specialty glass for these applications and ran across a couple of BBS posts that seemed to indicate some manufacturers actually did specify a different windshield for rain-sensing wiper equipped cars. It would be worthwhile to call a different independant glass place and ask if there is a special windshield for your car with rain-sensing wipers.

You mentioned they tested the system “in the shop” but that it does not work properly in actual rain. If they tested it indoors, then there was very little infrared energy that could interfere with the system operation. It works by ATR and expects nearly total reflection of the emitted energy if the windshield is clean and dry. When you go outside, there is significantly more background IR from the sun that could be fooling the sensor. Especially if the sensor is not coupled to the interior glass surface properly.

I’m waiting to hear about the “Special” $1500 windshield…Give-Me-A-Break…

Make someone at the dealership ride with you in a light rain. If they then agree with you that they don’t work right you then have some ammunition to use with the insurance co.Finding out if there are different spec. windshields might be important too, but I doubt if there are.I learned the hard way not to let my insurance co. pick my windshield company.

rdbulkley…the problem is the glass. Even though the glass is perfectly safe the aftermarket glass is a different thickness. The rain sensor detects moisture via refraction and since the glass is a different thickness the wipers do not operate properly.

Several years ago a local Lexus tech repaired a Lexus and took the vehicle out for a test drive. Even though he was a very good tech he made a mistake and at the end of the driveway he had the nose of the vehicle sticking out to far. A semi came by and was not able to swerve to avoid the Lexus. The semi destroyed the front of the vehicle including the windshield. I was hired to come out and write an estimate to repair the car. Under normal insurance guidelines a sublet glass was installed. The vehicle was completed and delivered and all was well until several weeks later it finally rained. The vehicle came back in and after a Lexus glass was installed the wipers worked correctly.

Now go back to the shop explain that the vehicle needs a factory glass and get a price since the insurance company will want to know. Now call the insurance company and explain that the sublet glass is causing the problem. Nobody did anything wrong here but a factory glass needs to be installed. A glass company will install the glass, the dealer will not.

Call the insurance company, explain the situation and post back. You should not owe a dime for this.