auto dimming rear view mirror - how do you know it works?

**brad** · 06-03-2015, 02:49 PM

post a photo. Sounds like it hasn't got it.

**DV52** · 06-03-2015, 10:39 PM

Originally Posted by brad

post a photo. Sounds like it hasn't got it.

brad: according to THIS, the 2014 Cross Polo 1.2 81kW DSG has an anti-dazzle mirror. So it should have a button that looks like this:

I know from experience that the anti-dazzle function won't work if the interior light is on- perhaps this is the problem (not sure)?

**wai** · 07-03-2015, 06:17 AM

The button is in the bottom near where the little green LED is. It is just about flush with the bottom of the mirror. You push it up from the bottom.

**KiwiME** · 07-03-2015, 06:35 AM

Thanks DV52 for actually looking that up! Yes, of course it has the feature, there certainly is no manual means to tilt the mirror and both sensors are present.

But it has neither the button nor the other feature just near it which I assume is the indicator light. The rear-facing sensor is at the top edge of the glass. Clearly it's a new design, the car is only a few months old. I can't find any setting anywhere in the Composition Media, or a button on the overhead console or the dash. Presumably it's fully automatic.

How close does a car need to be behind me to trigger it, and is it a gradual or sudden dimming?

Thanks for everyone who took the time to reply!

**DV52** · 07-03-2015, 08:29 AM

Originally Posted by KiwiME

Thanks DV52 for actually looking that up! Yes, of course it has the feature, there certainly is no manual means to tilt the mirror and both sensors are present.

But it has neither the button nor the other feature just near it which I assume is the indicator light. The rear-facing sensor is at the top edge of the glass. Clearly it's a new design, the car is only a few months old. I can't find any setting anywhere in the Composition Media, or a button on the overhead console or the dash. Presumably it's fully automatic.

How close does a car need to be behind me to trigger it, and is it a gradual or sudden dimming?

Thanks for everyone who took the time to reply!

kiwiME: hi again - hope that you are enjoying your new car

The anti-dazzle mirror on the two VWs that I have operate by what's called "a differencing method". Whilst it could be entirely possible that your mirror is not the same, I would be extremely surprised if the method was different in your new model.

My understanding is that there are "smarts" in the mirror that compare the amount of light falling on the front sensor (the one near the windscreen, looking forward) and the amount of light falling on the rear sensor (the one pointing to the rear of the car). If the rear sensor is seeing a much higher level than the front sensor, the mirror starts to dim (the glass on the mirror has a type of liquid-crystal display - just like display on calculators where the numbers appear in black). The more the difference in light levels between the front and rear sensors, the more dimming occurs. During daylight the difference between front and rear light levels isn't high. But, at night, there is virtually no light falling on either of the two sensors, so a moderate amount of light on the rear sensor makes the mirror dim.

So, the distance of the car behind isn't really that important except that the further away the car behind is, the lower the light level will be on the rear sensor. The only thing that is important for the mirror to dim is the relative light levels on the two sensors.

An easy way the check the operation of the anti-dazzle mirror is to put your finger over the front sensor. This will mean that no light at all is seen by the front sensor and pretty-much any light that falls on the rear sensor will cause the mirror to dim. Shining a torch on the rear sensor with your finger on the front sensor makes a dramatic effect!

On both my cars, I have changed the operation of the dimming function by placing a piece of black electrical tape over the front sensor (very low-tech method). When I want the mirror to dim, I simply switch-on the button and I get maximum dimming.

The final point that I would make is that the anti-dazzle mirror won't dim at all if the interior lights are switched-on (as I said in my previous post). If your car is fitted with LED interior lighting, it's sometimes not obvious that these lights are switched on because of the other lighting in the cabin (and because of the fact that LED lighting is extremely directional).

**KiwiME** · 07-03-2015, 08:56 AM

Thanks for the write-up, DV52. I've tried covering the front sensor and shining an LED light on the mirror-side sensor and nothing obvious happens (w/ ignition on.) I think I'll check the fuse first (53 under the dash, if I'm not mistaken) and then drive down to the local VW dealer and ask them if I can compare it to the same model Cross Polo they have on their lot.

**brad** · 07-03-2015, 09:35 AM

Wouldn't it be easier to just ask them to show you how it works? If they can't show you then it's obviously broken & a warranty issue.

**KiwiME** · 07-03-2015, 12:16 PM

Visited the VW dealer and my car and their car performed exactly the same. The effect is subtle (at least in daylight) but it definitely works. That's a relief since I would dread taking the car in for repair. The reason I didn't notice it in my tests in the garage is because the headlights were not "on" - a rather obvious point in hindsight.

Noting that the rear sensor is at the top of the mirror, the last time I was driving at night I noticed that headlights some ways back are shaded by the top of the rear window and that shadow darkens the area over the sensor. I wonder if that's why I don't see it changing? Is the sensor on the older type mirror at the top or bottom?

There is very little traffic at night where I live so I don't get many chances to try it out.

**DV52** · 07-03-2015, 01:21 PM

Originally Posted by KiwiME

Visited the VW dealer and my car and their car performed exactly the same. The effect is subtle (at least in daylight) but it definitely works. That's a relief since I would dread taking the car in for repair. The reason I didn't notice it in my tests in the garage is because the headlights were not "on" - a rather obvious point in hindsight.

Noting that the rear sensor is at the top of the mirror, the last time I was driving at night I noticed that headlights some ways back are shaded by the top of the rear window and that shadow darkens the area over the sensor. I wonder if that's why I don't see it changing? Is the sensor on the older type mirror at the top or bottom?

There is very little traffic at night where I live so I don't get many chances to try it out.

KiwiME: Sounds like success- well done!! Your model car is different from both my Golf and my Polo 6R in that the auto-dimming function on both my cars is not dependent on the light switch position (I just checked my Polo before writing this post).

Whilst I understand your logic in having tis way, on my cars the auto-dim will happen as long as the ignition is on (i.e. the anti-dazzle mirror must be supplied by a "terminal 15" fuse position) I'll look-up the wiring diagram to confirm this.