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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 02-15-2005, 07:09 PM
mandms7 mandms7 is offline
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Sensitivity Control For Auto Windshield Wipers

Is it just me, or does it seem like the sensitivity control for the auto windshield wipers don't do squat? On my 330Ci, I was adjusting the control in a light rain, and regardless of where I positioned it, there was no change in how frequently the wipers swept the windshield.
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Old 02-15-2005, 07:11 PM
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Hmm... I think it works for me on my '05 330ci... then again I've only had a chance to use it once.
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Old 02-15-2005, 08:29 PM
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I've had my car about 2 months and it hasn't rained that much, but I've noticed the same thing. Thinking about it though, I'm wondering how much difference between the positions there can actually be since the sensor is pretty small (i.e., small area of windshield scanned), and it would also depend on how the precip is hitting the glass, large drops spreading, small mist, etc... Today I was actually trying to remember which way to move the selector for high vs. low because wherever I put it the sweep cycle didn't really seem to change much.
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Old 02-15-2005, 08:34 PM
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Quote:
Originally Posted by markl53
I've had my car about 2 months and it hasn't rained that much, but I've noticed the same thing. Thinking about it though, I'm wondering how much difference between the positions there can actually be since the sensor is pretty small (i.e., small area of windshield scanned), and it would also depend on how the precip is hitting the glass, large drops spreading, small mist, etc... Today I was actually trying to remember which way to move the selector for high vs. low because wherever I put it the sweep cycle didn't really seem to change much.

If you start futzing with it, say, as you slow down off the road, while the speed sensitive part adjusts at the same time, you may not notice the difference. I think it works okay....

try it in a car-wash...
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Old 02-15-2005, 09:42 PM
SikUnt330Ci SikUnt330Ci is offline
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there is a slight change in the sensitivity for the auto wipers - unnoticable in heavy rain!
but in very light rain it seems like to work....slightly
the drops must hit the sensor surface...so probably on the lowest sensitivity it mite take 5 drops of rain on the sensor, instead of 1 drop on the sensor on highest sensitivity? who knows?
strange thing also if youve noticed... if you leave the wipers on auto, turn the car off and then back on, the auto-wipers dont work! unless u either adjust the sensitivity or turn if off and back on.
so practcially pointless in one way or another...
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  #6  
Old 02-15-2005, 11:08 PM
BMW_Brand BMW_Brand is offline
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Quote:
Originally Posted by SikUnt330Ci
there is a slight change in the sensitivity for the auto wipers - unnoticable in heavy rain!
but in very light rain it seems like to work....slightly
the drops must hit the sensor surface...so probably on the lowest sensitivity it mite take 5 drops of rain on the sensor, instead of 1 drop on the sensor on highest sensitivity? who knows?
strange thing also if youve noticed... if you leave the wipers on auto, turn the car off and then back on, the auto-wipers dont work! unless u either adjust the sensitivity or turn if off and back on.
so practcially pointless in one way or another...


I completely agree-- I usually keep mine on the least-sensitive setting. It bugs me when the wipers wipe across when there is very little rain on the windshield and it makes that horrid "schreeetcch" sound.
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Old 02-15-2005, 11:49 PM
allaboutme allaboutme is offline
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Quote:
Originally Posted by SikUnt330Ci
you leave the wipers on auto, turn the car off and then back on, the auto-wipers dont work! unless u either adjust the sensitivity or turn if off and back on.
so practcially pointless in one way or another...
I think that's to prevent accidents along the lines of going through a car wash.
I don't think auto wiper's purpose is to never have to turn them on. I think it's so you don't have to adjust the sweep intervals. That's what is so marvelous about them.
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Old 02-16-2005, 12:38 AM
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Having to turn it on each time you start the car is a design feature, so the wipers aren't damaged by car wash or accumulated snow/ice.

If water is accumulating on the windshield at a high enough rate, the wipers go to continuous mode, and the knob no longer controls wipe frequency. (Presumably, it also determine when to go to fast wipe? )

Vehicle speed does not factor into the wiping algorithm on rain-sensor cars (at least according to the E46 training manual, revision 11/22/00).

If the rain sensor is broken (the system has a self-diagnostic), the wipers operate purely as intermittent wipers, with wipe frequency controlled by the knob. If your knob is broken, the setting 3 delay value is used (4 - being most sensitive/least delay).

Next time you wash your car, you can find out if the sensitivity control is working. Have someone else hold a light, controlled spray of water on your windshield while you sit in your car with the key in position I, and test it.
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  #9  
Old 02-16-2005, 03:08 AM
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Quote:
Originally Posted by FenPhen
Having to turn it on each time you start the car is a design feature, so the wipers aren't damaged by car wash or accumulated snow/ice.
Exactly. Every time I think I know all there is to know about this car, I learn something new. In particular, the rear wiper goes to intermittent mode if left switched on - but if you put the car in reverse, the rear wiper goes to full speed until you take the car out of reverse. Clever...
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Old 02-16-2005, 05:18 AM
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Quote:
Originally Posted by FenPhen
If water is accumulating on the windshield at a high enough rate, the wipers go to continuous mode, and the knob no longer controls wipe frequency. (Presumably, it also determine when to go to fast wipe? )
We get enough rain over here in Germany to test that out... I have been in the car quite a few times when the rain was heavy enough to trigger "full speed" on the wipers...
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  #11  
Old 02-16-2005, 06:13 AM
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My previous car had rainsense wipers but no sensitivity control. Regardless, rainsense is the best thing that's come along IMO for wiper control. I was always so frustrated by constantly adjusting the wipe frequency with standard intermittent wipers. It's so cool when you come to a stop in very light rain and they just wait until you start going again. When I drive my wife's '03 TL (doesn't have rainsense!), it' such a pain...
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  #12  
Old 02-16-2005, 06:35 AM
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Quote:
Originally Posted by markl53
Thinking about it though, I'm wondering how much difference between the positions there can actually be since the sensor is pretty small (i.e., small area of windshield scanned)...
Actually the sensor size has nothing to do with it. The The sensor does NOT measure just the area of the sensor. That wouldn't do much good, since it is in the rearview mirror mounting area, wich does not get wiped by the wiper.
The way this sensor works is:
-The sensor discharges a measured amount of infrared light into the glass.
-The infrared light bounces around in the glass.
-The sensors sets a baseline on how much infrared light it should see in the glass(the reason for the initial wipe when you change sensitivity levels.)
-When a water droplet sits on the glass, it changes the optical property of the glass (an escape route for light), so when the infrared light hits the area of the glass with a water droplet on it, it leaves the glass at that point.(Ibet this would be a pretty neat light show with night vision goggles)
-Now the sensor no longer "see's" the sameamount of infrared light bouncing around inside the glass, so it triggers the wipers to clear the water droplets (escape routes for the IR light)
-Just the opposite occurs when less water droplets are on the window. The sensor starts "seeing" more and more light bouncing around inside the glass again, so it tells the wipers to slow down. Or if it reaches it's baseline(from right after initializing wipe)again they shut off.

Last edited by Test_Engineer; 02-16-2005 at 06:37 AM.
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  #13  
Old 02-16-2005, 06:37 AM
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Quote:
Originally Posted by Test_Engineer
Actually the sensor size has nothing to do with it. The The sensor does NOT measure just the area of the sensor. That wouldn't do much good, since it is in the rearview mirror mounting area, wich does not get wiped by the wiper.
The way this sensor works is:
-The sensor discharges a measured amount of infrared light into the glass.
-The infrared light bounces around in the glass.
-The sensors sets a baseline on how much infrared light it should see in the glass(the reason for the initial wipe when you change sensitivity levels.)
-When a water droplet sits on the glass, it changes the optical property of the glass (an escape route for light), so when the infrared light hits the area of the glass with a water droplet on it, it leaves the glass at that point.
-Now the sensor no longer "see's" the sameamount of infrared light bouncing around inside the glass, so it triggers the wipers to clear the water droplets (escape routes for the IR light)
-Just the opposite occurs when less water droplets are on the window. The sensor starts "seeing" more and more light bouncing around inside the glass again, so it tells the wipers to slow down. Or if it reaches it's baseline(from right after initializing wipe)again they shut off.
Thank you, that is the most informative post I've seen in about a month
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Old 02-16-2005, 07:53 AM
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Mine works perfectly. Don't use any RainX stuff.
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  #15  
Old 02-16-2005, 08:03 AM
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I was just thinking about this the other day. The knob doesn't seem to do anything.
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Old 02-16-2005, 08:16 AM
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Mine works fine. You only notice it if the rain is light.
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Old 02-16-2005, 12:22 PM
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If your car has the rain sensor the thumbwheel knob only activates the sensor. In cars without the rain sensor knob should regulate the wiper interval. The wiper stalk has five positions: off, up one position for interval wipe/ activate the rain sensor, up two positions for slow steady wipe, up three positions for fast steady wipe, and down one position from off for a driver/manual controlled wipe. As mentioned previously you have to activate the rain sensor each time you start the car, and the interval is determined by the sensor not the thumbwheel switch.

With the rain sensor you can leave the stalk in position 1, but after you shut off the ignition you'll have to reactivate the sensor either by moving the interval knob, or recycling the stalk between off and first position. Remember to turn off the sensor before going through a car wash.

An interesting discovery on my part is that the sensor will move the wipers faster in a cloud burst than if you select the number 3 fast position.
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Old 02-16-2005, 12:53 PM
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another way I figured my sensor was working was simply pulling into my garage. Here in LA we had that crazy week long storm...I would drive in the downpour wipers going full speed, pull into the garage...2 wipes later..OFF.

LOVE THAT!
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Old 02-16-2005, 04:20 PM
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Quote:
Originally Posted by HUMMM 3
If your car has the rain sensor the thumbwheel knob only activates the sensor. In cars without the rain sensor knob should regulate the wiper interval. The wiper stalk has five positions: off, up one position for interval wipe/ activate the rain sensor, up two positions for slow steady wipe, up three positions for fast steady wipe, and down one position from off for a driver/manual controlled wipe. As mentioned previously you have to activate the rain sensor each time you start the car, and the interval is determined by the sensor not the thumbwheel switch.
See page 77 in the owner's manual. It specifically states that the thumbwheel can be used to set the sensitivity of the rain sensor. In non-rainsense cars, it controls the timing of the delay interval.

The thumbwheel allows you to vary, within what seems a small range, the sensitivity level of the rain sensor to control how much water on the windshield is "tolerated" before it calls for a wipe.
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Old 02-16-2005, 04:27 PM
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Quote:
Originally Posted by Test_Engineer
Actually the sensor size has nothing to do with it. The The sensor does NOT measure just the area of the sensor.
True, the sensor measures an area larger than the sensor itself, since it shines an IR beam toward the glass, but there is a compromise on sensor size for aesthetic reasons vs. the size of the area of the glass which is sensed. I still maintain that the area sensed is small enough to constrain the effect of the sensitivity control.
Quote:
That wouldn't do much good, since it is in the rearview mirror mounting area, wich does not get wiped by the wiper.
I assume you meant that you don't think the area of the windshield where the sensor is mounted is covered by the sweep of the wiper. In fact, the right hand wiper does sweep over the area where the sensor is mounted near the rear view mirror. The sensor couldn't do it's job properly otherwise.
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Last edited by markl53; 02-16-2005 at 04:35 PM.
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Old 02-16-2005, 07:42 PM
mandms7 mandms7 is offline
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Well at least some people are agreeing with me. In hard rain I agree that the sensitivity wouldn't make a difference, but I was adjusting the sensitivity in very light rain, and it didn't make any difference where I turned the dial.
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Old 02-16-2005, 09:25 PM
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Quote:
Originally Posted by mandms7
Well at least some people are agreeing with me. In hard rain I agree that the sensitivity wouldn't make a difference, but I was adjusting the sensitivity in very light rain, and it didn't make any difference where I turned the dial.
Same here. No noticeable difference to me when I change the "sensitivity" setting in either light or heavy rain.
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Old 02-16-2005, 11:43 PM
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Quote:
Originally Posted by Test_Engineer
Actually the sensor size has nothing to do with it. The The sensor does NOT measure just the area of the sensor. That wouldn't do much good, since it is in the rearview mirror mounting area, wich does not get wiped by the wiper.
The rain is only measured in the sensor area (the black square where the rear view mirror attaches to the windshield).

The sensor area has an infrared emitter, reflector, and detector. The emitter shoots the beam at an angle into the windshield, the beam bounces off the density difference between the glass and outside air, then off the reflector (which is pressed against the inside of the windshield), off the glass-air boundary again, until it reaches the detector.

Water or dirt on the sensor area has a density closer to the glass than the air, and so part of the light travels past the glass, and is refracted, so less light hits the detector. The angle and distance from the emitter to the detector has to be fixed and known, so the sensor area can't be that large.
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Old 02-17-2005, 12:06 AM
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Old 02-17-2005, 12:44 AM
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