How does the car know when it's raining?

[Dash]

Yeah, I know that seems like a crazy question but if I leave my wipers on intermediate low and it stops raining, they will stop moving... But if it starts to rain again (even a little) they will kick back on.

My question is, what sensor does the car use? Is it a microphone, impact sensor, magic?

My most resent experience with this actually happened at a track day that started out wet in the early morning. Doing about 115 down the front straight, it started to rain just slightly (like 10 drops) I had forgotten that the wipers were on at all and bam... there they go. Not that it was a big deal, but it sure was unexpected.

[b8audis4]

It is a sensor on the windshield. It is on the mirror. Uses light I believe.

[Over9000]

It is a sensor on the windshield. It is on the mirror. Uses light I believe.

Correct. Infrared. It shoots into the windshield at a 45° angle and alters wiper speed based on how much of that is reflected back on the sensor. Rain droplets disrupt the normal reflection back to the sensor from the surface of the windshield.

[Pilfer]

Correct. Infrared. It shoots into the windshield at a 45° angle and alters wiper speed based on how much of that is reflected back on the sensor. Rain droplets disrupt the normal reflection back to the sensor from the surface of the windshield.

[MarcWinkman]

Correct. Infrared. It shoots into the windshield at a 45° angle and alters wiper speed based on how much of that is reflected back on the sensor. Rain droplets disrupt the normal reflection back to the sensor from the surface of the windshield.

...Soooo, it's witchcraft

[Over9000]

...Soooo, it's witchcraft

Essentially, yes.

[SteveYem]

Essentially, yes.

Hypothetically, if there was crack or some other permanent blemish or discontinuity in the glass right where that sensor is looking for that reflection, could it cause the system to think there is always water on the glass?

[AudiTFSI3o3]

Correct. Infrared. It shoots into the windshield at a 45° angle and alters wiper speed based on how much of that is reflected back on the sensor. Rain droplets disrupt the normal reflection back to the sensor from the surface of the windshield.

also, you need to change your avatar to DBZ, or atleast Vegeta. that is all.

[Over9000]

also, you need to change your avatar to DBZ, or atleast Vegeta. that is all.

LOL Someone got it!

[MrFunk]

Auto Rain Sensor Wipers have been around for ages. In the 50's they had a rain sensor in some american convertible to trigger the top to close if it started raining. I know my friend's Acura has that also - if he leaves the sunroof open after he parks and leaves the car, it will shut itself it it starts to rain. Would be nice if ours did that also - doubt it does...

[VenturiRS]

Auto Rain Sensor Wipers have been around for ages. In the 50's they had a rain sensor in some american convertible to trigger the top to close if it started raining. I know my friend's Acura has that also - if he leaves the sunroof open after he parks and leaves the car, it will shut itself it it starts to rain. Would be nice if ours did that also - doubt it does...

You wanna experiment for us?

[Dash]

You wanna experiment for us?

Well, you could just do it in the garage with a spray bottle of water.

[amz]

You wanna experiment for us?

This can be coded into some/most VW's with rainsensors, but for some reason, not for Audi. Audi has a weird phobia of things closing on their own.

[SteveYem]

You wanna experiment for us?

I unintentionally experimented with this last summer at work during a torrential downpour. I was in the office, the car was in the parking lot.
The moonroof does not close itself when rain hits the roof.

[drob23]

I unintentionally experimented with this last summer at work during a torrential downpour. I was in the office, the car was in the parking lot.
The moonroof does not close itself when rain hits the roof.

Sacrificed for science!!!

[SteveYem]

Sacrificed for science!!!

I also concluded from this experiment that my shirt and pants get saturated, and I look like a silly person, when sprinting out the front door of the office toward my car during said torrential downpour.

[Dash]

Cool. Thanks for the replies guys!

[Pilfer]

I feel that sometimes happens when I'm at a stop light. It won't wipe the windows unless I'm moving sometimes. Of course moving to CA so windshield wipers are no longer needed :/

[jasonE30m3]

Cracks in the windsheild don't seem to efffect the rain sensor working properly. I got hit with a rock on the highway a couple weeks ago and got a huge chip. With the change in weather over the past week the crack has gone across my whole windshield. Havent had any problems with the rain sensor not working correctly.

That reminds me I need to call my insurance company and get the thing replaced.

[esimp2k]

I think the op's suggestion of magic is better. expecto-rain! Kids are all about magic movies lately.

[Black_V!per]

I think the op's suggestion of magic is better. expecto-rain! Kids are all about magic movies lately.

Mine gets the information from weather.com using my exact GPS coordinates coupled with the cars 3G connection. Sometimes it misses and I drive a few miles without them on, 3G is slow and weather.com is bloated with crap-ads.

In seriousnisity, I've had bugs turn the wipers on. Went through a shit storm of gnatts or something and wipers smeared their guts all over the window, had to use like 9 shots of wiper fluid to see. Annoying as much as it is a blessing sometimes.

[Dash]

In seriousnisity, I've had bugs turn the wipers on. Went through a shit storm of gnatts or something and wipers smeared their guts all over the window, had to use like 9 shots of wiper fluid to see. Annoying as much as it is a blessing sometimes.

That would be annoying... and gross.