Odd Triggering Of Auto Wipers

[chezwot]

Yesterday I drove along a route I haven't used before and on passing over a bridge my wipers started working although it was a clear bright, dry sunny day. On returning along the same route, at the same spot the wipers came on again, any ideas?

[craggle]

The wiper sensor is a small rectangle area to the right hand side of the interior mirror and can be seen quite clearly from outside the vehicle.

It works by shining an infrared LED at the surface of the glass and if the windscreen is nice and clear the beam gets reflected back into a sensor. When rain hits the window the beam is dispersed by the rain drops so the return to the sensor reduces and when it hits a low level the wipers turn on to clear the screen.

I have found the wipers turning on at funny times too and always found dirt, dead flies, bugs Etc stuck to the screen in the sensor area. Clean them off and the wipers wont come on again.

I now tend to keep my wiper stalk in the off position and turn them to auto when it's raining, saves the dry wiper blade scratching it's way across the glass.

Craig.

[chezwot]

I had cleaned the car prior to using it and there were no insects, bugs etc on the windscreen. What I found strange was that the event occured in the exact same place each time. I am going on that route again later today and it will be interesting to see if it happens again. There are no factories or other forms of commercial buildings in the area as the bridge is in the countryside therefore ruling out the possibility of interference from some form of transmitter/radiation etc.

[craggle]

Don't think there is anything in the system to be interfered with? Maybe lighting conditions can do it but strange it happened in the same place, could be coincidence but interesting to hear if it happens again.

Wasn't a bridge over a stream with still water and lots of flies above it? If you hit that many flies though both times I guess there would be some evidence! :)

Another reason I started keeping my wipers in the off position was when we had frosty and frozen mornings. I often wondered what would happen if I jumped in, started the car to warm it up and the wipers tried to automatically clear the screen while frozen solid to the screen? Not sure if there is an overload limit on them or if they would bend the arms or blow the fuse?

Let us know what happens tonight. :)

Craig.

[chezwot]

Just back from repeating the journey and this time both ways over the bridge, which is over a motorway, nothing happened. The first time I would not have taken any notice except my wife asked why I had switched on the wipers and she was the one who noticed that they had operated again in the very same place - very odd! We don't have frosty frozen mornings here but I'll take your advice and leave the auto off until it rains.

[tarquin]

It can be low sun angles, As the sun's light skips across the upper atmosphere,it acts like a prism, refracting white light to its basic components, including ultra violet and infra red. Could be its dispersal across the windscreen tricked the sensor into thinking its beam scattered across the glass and triggered the wipers. It happened to me occasionally on sunny mornings. In days gone by when we had the first remote car alarms, they were infra red key fobs. and often on bright days you would have to shield the sensor in the car windscreen from the sun to operate it by putting your hand over it. Also if your sitting in your living room and the sun is pouring in through the window , it can be difficult to operate the TV remote for the same reason.

David