I was installing a dash camera the other day and noticed a sensor behind the passenger side of the rear view mirror. Can anyone tell me what this does? Is it the daylight sensor? I tried my best not to block it.

 

My 2011 Chevy has the sensor at the base of the windshield. A small kind of clear looking dome just sitting there. Since I haven't spotted the same thing at the base of the windshield on my Jag, I would figure the next best spot would be hidden behind the mirror. Soon I'll look into the rain sensor that has me curious.

 

My guess would be that’s it’s probably for the auto head light dipping

 

My 2011 mirror has it's own sensor so it can know it's night and can change the mirror when it senses a cars headlights on your tail as well. Mine came with just the on star on the mirror. With the other mirrors being self contained I was able to get one with reading lights, auto changing, compass, as well as on star. It simply plugged in and works fine.

 

So no one knows what it does? The auto high beams I am pretty sure use the camera mounted where the mirror connects with the window. I suspect this is probably just a daylight sensor.

 

FWIW, when I had my radar detector mounted just below the rearview (obstructing the sensor), the auto high beam dipping did not work correctly. After moving it low on the windshield, it works fine.

 

Interesting. But I don't think that is the auto-dip sensor. Mine will detect a taillight 1/2 mile ahead of me there is no way a light sensor could do that. It also discerns between street lamps and headlights. It seems like they are using the windshield camera to intelligently analyze the view. I am pretty sure that camera also analyzes the windshield for raindrops for the auto-wipers. Perhaps I should just cover it up with tape and see what stops working.

 

Actually, I found a good diagram. The light/rain sensor is a combined unit near the mirror. The auto dip is a sensor located IN the body of the mirror.

 

#1 is what I thought it was then. And the rain sensor I thought was the GPS box maybe. Still nothing to say what that mirror sensor is. Weird. Thanks for posting!

 

It may be the auto dipping, for the rear view mirror. If you place your finger over it (The sensor) The mirror should start to dim. You can try this in the daytime. If it doesn't dim, then it's the dimming sensor. That's my guess anyway.
Hope it helps.

Alan

 

Sorry
If it doesn't dim, then it's NOT the dimming sensor.

 

I also have a correction. The Jaguar does have a sensor at the base of the windshield, for the "auto headlights" I would assume. Just like my 2011 Chevy.
It's hidden by the slope of the dash.

 

The domed sensor at the base of the windscreen is the solar sensor which is used by the automatic climate control system to accommodate the heat gained through the glass.

I'm not sure which sensor the OP is referring as there are a couple around that area. The light sensor for the auto-dim/electrochromic mirrors is on the driver-facing side of the mirror (look for little shiny dot at the bottom). The camera for the AHB/auto-dip full beam headlights is on the rear in the masked glass area, and visible as a little camera lens if you shine a light in from outside. There is also a humidity sensor that is used by the climate control system to automatically defog the glass, and the rain sensor photodiodes which sit flush against the glass and measure the internal reflection of an IR beam bounced around inside the glass.

 

It is a sensor on the actual mirror near the bottom of the mirror but on the passenger side, not the driver side. I would not think this is for the auto-dim mirror since that would need to have light sensed from behind the car.

 

[QUOTE=JagGate;1837324]It is a sensor on the actual mirror near the bottom of the mirror but on the passenger side, not the driver side. I would not think this is for the auto-dim mirror since that would need to have light sensed from behind the car.[/QUOT

There are two sensors on the mirror. one on the back and one on the front. If the light is brighter facing the mirror, IE a car headlights from the rear, at night. Then the mirror dims. It shouldn't dim in daylight, as the light is brighter from the back of the mirror. Like I have already said. To find the sensor. Simply place your finger/hand over the sensor at the back of the mirror, during the daylight. It should then dim the mirror. I don't think there is a sensor at the rear of the car to enable the dimming of the mirror.

 

“I know you think you understand what you thought I said, but I'm not sure you realize that what you heard is not what I meant.” Alan Greenspan, former Chairman of the Federal Reserve.

You're both right and wrong because what xdave explained was ambiguous. My favorite example of an ambiguous statement is "John mopped the floor with Fred". Here's poor Fred:



Whether the sensor is on the driver's or passenger's side depends on whether the car is RHD or LHD. Because you're in the USA, your XJ is LHD; since xdave is in the UK, his XJ is RHD. In any case, that sensor is near the bottom right side of the mirror, regardless of being RHD or LHD, and senses headlights from cars behind you.

Stuart

 

Poor Fred!

As Alan mentions, that sounds like the ambient light sensor which turns on your auto dipped beam headlamps/interior button lights/etc, and is compared to the light from the rear to activate the electrochromic mirrors when needed. It would have a clear plastic cover. Unless you are tightly blocking it your dash cam probably won't affect it. In my head I thought you were talking about a sensor behind the stem cover, but of course that doesn't make sense as you can't fit an aftermarket dash cam in that space. Only the ambient light and rear-facing sensors are mounted on the mirror body itself.

It is worth noting that most of the actual mirrors fitted in our X351s pre-2016MY (when the new vision system was introduced) are model-unspecific shared parts across many Jags and Range Rovers and the sensor positions do vary depending on which one you have in your car. The USA get an additional option of a garage door/radio opener which changes the location of the ambient sensor to the edge of the mirror and it is more oblong. The rear-facing dot could be either in the mirror glass itself or in the plastic surround. I've seen a photo with that green LED compass the US market likes displayed in the corner of the glass too so either that has been an option at some point, or someone has fitted an X350 mirror to their car.

 

This is finally making sense thanks!

I think Jaguar needs a new motto:

Jaguar: Redesigning even the most simple of things.....