What's the sensor for?

**krazylegz** · 30th March 2012, 15:18

Just noticed a sensor on the windscreen, inside the interior mirror casing.

Does anyone know what it's for, rain sensitive wipers or something?

**cont1204** · 30th March 2012, 15:32

Rain sensitive wipers.

**Ian-Highlander** · 30th March 2012, 15:33

There can be two sensors visible from outside just infront of your rear view mirror depending on the spec of the car. One is for auto wipers, one is for auto headlights.

**krazylegz** · 30th March 2012, 15:51

Ah right cheers lads, surprised mine has them on as it's only a sxi.

Take it the wipers need to be in the first position for them to be on auto?

**rich r** · 30th March 2012, 18:15

Also,

Sensor on the back of the mirror housing itself (facing windscreen) is for the ambient lighting (on the bottom of the mirror housing).

Sensor on the front of the mirror (facing the interior of the car) is for the auto-dimming function of the mirror.

**Handyandy-UK** · 30th March 2012, 20:47

Originally Posted by rich r

Also,

Sensor on the back of the mirror housing itself (facing windscreen) is for the ambient lighting (on the bottom of the mirror housing).

Sensor on the front of the mirror (facing the interior of the car) is for the auto-dimming function of the mirror.

Not quite .... the difference between the light levels detected by the front and rear facing sensors determines how much the self-dip function darkens.

The down facing ambient light is the same intensity all the time when the vehicle lights are on.

**Ian-Highlander** · 31st March 2012, 11:12

Originally Posted by Handyandy-UK

Not quite .... the difference between the light levels detected by the front and rear facing sensors determines how much the self-dip function darkens.

The down facing ambient light is the same intensity all the time when the vehicle lights are on.

Ambient lighting only comes on in the dark if the lights are on, not just with vehicle lights. Try it, switch your headlights on in the daylight and your ambient lighting won't come on.

**rich r** · 2nd April 2012, 09:13

Indeed - it has to be dark for the ambient lighting to come on, so it must use the sensor in the mirror housing. If you put your headlights on when it's not dark (eg for fog/rain) it doesn't come on.

**Big Dave** · 2nd April 2012, 10:30

Originally Posted by rich r

Indeed - it has to be dark for the ambient lighting to come on, so it must use the sensor in the mirror housing..

It uses the sensor on the back of the mirror. Try covering it with tape and the little LED under the mirror will come on, regardless whether headlights are on or off.

**Z80** · 26th May 2012, 08:22

Yes, that's the point.

I was seriously thinking on adding an automatic headlights feature using that sensor.

I just don't know if it would trigger faster enough, though.

Th other alternative would have been to change the windscreen to a dual sensor model when it had to be replaced, but I just forgot to ask for it. Now I have to wait for someone breaking my windscreen again !