Can anyone tell me what the sensor behind the windshield rear view mirror is for?
2017 RDX Elite.

 

You're going to have to be more specific. There are multiple sensors, IR sensor for the automatic windshield wiper, or the camera for the lane assist/vehicle tracking. Or the sensor on the rear view mirror that dims the mirror when someon uses their brights behind you.

 

I only see one sensor behind the mirror... here's a picture of it. Looking at the mirror from the outside, it's on the drivers side of the mirror.

 

The reason I'm asking is I mounted a Dash Cam to my windshield in front of it without realizing there was a sensor it would be blocking. It doesn't seem to affect anything obvious, but would like to know if I have to re-located the dash cam.

 

Although the owners manual does not describe the purpose of this sensor, "I think" it is used to determine the amount of light coming into the windshield from the front of the vehicle. The amount of light coming in the rear windows is determined by the sensor on the front side of the mirror.

If it is dark in the front of the vehicle, and bright in the rear, then the system determines it is nighttime and another car is following, so the mirrors will dim to prevent blinding the driver.

I think if you block this sensor, so that it looks dark in the front, then the mirrors may dim during regular daytime driving (because the rear sensor sees lots of light) which will reduce the visibility in all your rear-view mirrors.

It really depends on how much light your new cameras is blocking.

EDIT: I just had a thought that if this is a light sensor, it may also be used to determine when your headlights turn on automatically. You might want to put some black tape over the sensor and see if you notice anything abnormal with the headlights or rear view mirrors.

 

OK, thanks for your input... very much appreciated !!
When we get a bright and sunny day, I'll try the tape trick and see what happens.

 

According to the video the sensor on the mirror is the glare sensor and the one you're asking about is the ambient light sensor. They work together to dim your mirror.

 

Thanks you!! Amazing technology.... Since this our first vehicle with auto dimming features, it's makes me wonder how we got along before.

 

You had a prismatic mirror - which worked better. My experience with the interior mirror is that the dimmer does almost nothing, whereas the outside mirrors work great.

 

Yup, the good old days. My comment "makes me wonder how we got along before" was with "tongue in cheek"
I would rather have the old style myself.....

Today was a sunny day, so I went for a short drive and placed my hand over the mirror sensor, and yes, both side mirrors and the rear view mirror dimmed. It took a few seconds to respond but the difference is quite noticeable.
Next time, I'm going to unplug the harness that feeds into the rear view mirror and for a night drive. To be continued........

 

Charlie:

Can you post a picture as to how you have mounted the dashcam?

Any updates to your lastest tests?

Thx...

 

I stalled a Viofo A119 in my RDX. It hides well without affecting any vehicle sensors.