Sensor behind rear vision mirror?

[neerav]

Does anyone know what this circled area on the back of the rear vision mirror of my Aussie MG4 Long Range 77 MY24 is?

My guess is some kind of sensor

I'm not sure if I should install my dashcam stuck onto the windshield in a place that could block this possible sensor, or it doesn't matter

 

[Ian Key]

Could be the sensor for the auto dipping of the headlights when there's oncoming traffic.

 

[webhiker]

Could be the sensor for the auto dipping of the headlights when there's oncoming traffic.

 

[PeteC]

Could it be some kind of sensor for the auto dimming of the mirror?

 

[Kithmo]

My guess is it's the daylight sensor for the auto dipping mirror. The glare sensor is on the mirror side.

 

[leonkernan]

Whatever it is, it's not on the Excite's mirror, so it's not the main light sensor.

 

[neerav]

Whatever it is, it's not on the Excite's mirror, so it's not the main light sensor.

Intriguing thanks Leon

 

[wattmatters]

Essence and LR77 models have an auto dim rear view mirror, Excite models do not.

 

[neerav]

Essence and LR77 models have an auto dim rear view mirror, Excite models do not.

View attachment 27616

I think you've might have solved it

 

[Flightengineer]

Essence and LR77 models have an auto dim rear view mirror, Excite models do not.

I think you mistaken. Dim rear mirror sensor positioned looking aft. You can see it from driver seat. Topic starter asking about other sensor which is looking forward. And this sensor visible only through windshield.

 

[wattmatters]

I think you mistaken. Dim rear mirror sensor positioned looking aft. You can see it from driver seat. Topic starter asking about other sensor which is looking forward. And this sensor visible only through windshield.

It senses light from both directions and determines the difference in light level between fore and aft. That difference is used to control the dimming function.

While MG don't have an explanation, another manufacturer, SEAT, do:

Rear view Mirror, autodimming
The auto-dimming rear view mirror offers greater safety when driving at night, as it stops you from being dazzled by traffic travelling behind. It consists of a mirror element and an electronic system that detects light from in front and behind by means of photo sensors. If the amount of light from behind is greater than that in front, the mirror is darkened. The surface of the mirror features a layer of electrolytes, similar to the LCD display of a mobile phone. The electrolytes consist of uniform crystals. When a voltage is applied, the crystals arrange themselves at a given angle, determining how much light is reflected. The strength of the voltage determines to what extent the mirror is darkened.

 

[neerav]

I got an answer from a contact at MG Australia HQ

"The sensor in the rear of the mirror is an ambient light sensor for the self dimming mirror, it’s not sensitive to items in front of it. So you can fit a camera in front of it without affecting its operation."

 

[wattmatters]

I got an answer from a contact at MG Australia HQ

"The sensor in the rear of the mirror is an ambient light sensor for the self dimming mirror, it’s not sensitive to items in front of it. So you can fit a camera in front of it without affecting it’s operation."

Interesting. It still leaves your original question unanswered - what is that front sensor for then?

 

[neerav]

Interesting. It still leaves your original question unanswered - what is that front sensor for then?

I was only interested in the rear mirror sensor so my question is answered

 

[bedsev]

In other cars I've had it's a sensor for the autodimmering mirror, if you put a dashcam in front of it the mirror doesn't work properly

 

[wattmatters]

I was only interested in the rear mirror sensor so my question is answered

Ah, just re-read what you wrote - "rear of the mirror" meaning on the opposite side to the mirror. I was originally thinking it meant the sensor in the mirror facing the rear.

I fail to see how blocking a light sensor would not affect its operation but I guess it depends on how much light is being blocked.

 

[Kithmo]

If you block the ambient light hitting the front sensor, the mirror will dim because the rear sensor is getting more light.
You can see this if you cover the front sensor with your finger and if you shine a torch on it the mirror brightens up.
Putting a dash cam there could result in a darker mirror depending how much light it's blocking.
FWIW, it's slow to react.