What's this little black box?

If you have a voltmeter, you can see if one of the leads is live all the time, or comes on only when you cycle different systems (lights, wipers, AC, defrost). That might help you figure out to which system it belongs.

 

There's power on the dome light wires, but it's on all the time. I suspect you want power that's only active when the car is in ready mode. Some dash cams have voltage detect and can shut down when the battery is no longer under charge. I don't know about radar detectors. Then again most Prius drivers don't need radar detectors.

 

For those interested in how to answer this kind of question by looking on TIS, you can pull up the electrical wiring diagram (EWD) and start in the Location & Routing section, and choose Body. You get a drawing of the body showing the rough position of all the gizmos in it, with circles and arrows:



You can see (look at the 1234 at the bottom) there are four pages of this, and O1 (the circle in red because I clicked it) is on page 3. All four pages show the same diagram and the same gizmos, they just can't fit all the circles and arrows on one page, so you click through the pages until there's a circle and arrow pointing at the thing you want to know about.

Because I selected O1, the orange info button down in the lower right corner lights up. Click that, and you get to see the electrical connector specs and what it is for. (Caution: the part number shown here is not for the sensor itself; it's for that black plastic 4-position connector on the wire harness, in case it ever needs replaced. You can also click the Wire Harness Repair link for the part number and specs of the wire terminals used in it.)


(in fact, just hovering the mouse over O1 on the location page makes "Rain Sensor" appear next to it.)

There are some links at the bottom there. The Location link, Body Position of Parts will just go right back where we came from. But one of the System links, Front Wiper and Washer (w/ Auto Wiper System), goes to the circuit diagram, with the item in question blinking red:



... and there it shows the same wire colors shown in your photo, so it looks like we've got a positive ID. If you browse further around the diagram, you see that the W-B wire is ground, and the LG one is IGnition switched through a 10 A fuse.

How much additional draw you'd want to add on that circuit would depend on spending a little more time following the circuits that start at that same fuse, to learn how much stuff is already on it, which could be an easy exercise for the reader.

-Chap

 

I have both the camera and this box. I don't have the rain sensor. So I also was asking myself what it is. For being a humidity sensor, it is quite a big box. And my cars gets fogged windows more than on the Gen3... So likely it is a box for that and the rain sensor, and when not equipped, same box for the humidity sensor only.

 

If the box you have is the same one shown in the original poster's photo, with the same connector and attached to the same color wires, then the only mystery is why you think you don't have the rain sensor. It was identified in post #23.

-Chap

 

If you are referring to my post, and not the OP, no - I don't have a rain sensor. It is not offered as an option in my trim level here in Germany. And my windshield wiper controls, don't show the "auto" word anywhere. I used to have it in Gen3 (as an option) and I miss it. I have regular windshield wiper control. And intermittent is "beautifully" manual...
If they mount the sensor in any case, or for also another use, I don't know. I for certain have this same box and I posted about it in another thread, asking exactly the same question:
What is the sensor/device next to the front camera? | PriusChat

From what I read in that thread, Toyota uses the same box for rain sensing and humidity sensing. Even if the rain sensor is not there physically or there, but disabled.
Though I don't think it works too well, since I often have fogged windows and nothing happens, unless *I* set the AC to "defrost" (front *and* back). Compared to Gen3, this Gen4 gets fogged windows more often.

 

Perhaps because the owners manual expressly states otherwise?

 

That manual page also advises against running the AC off the 12 Volt battery; I'm a believer

 

I don't have the Auto rain sensor either. Everything in my car is manual.
So what does that "humidity sensor" supposed to do? When does it kick in? Does the HVAC have to be set in Auto Mode or something? (I never use that either. )

 

That seems to be the secret: the same part number is shown for all Prius trim levels, including those without automatic wipers.

It seems to be an optical sensor looking for refraction due to moisture on the windshield. In the higher trim levels, the automatic wipers can be triggered by it. Otherwise, it is apparently still used by the HVAC.

This is reminiscent of Gen 3's sunload sensor, which lives on the right side of the dash, and in all trim levels it influences the HVAC blower, but only in some cars is it also used for automatic headlight control.

-Chap

 

There's probably a limit to how many BLACK BOXES you can put on a windscreen - so maybe they've doubled up.

 

Maybe it turns out that an optical device for detecting moisture on a windshield is also good for detecting moisture on a windshield.

-Chap

 

according to the manual this box may serve 2 purpose:
1. The side faced windshield may be equipped with optical sensor for automatic wipers.
2. On the right side of this box the humidity sensor is located.

 

They cleaned up the exposed wires on the 2017.
My Trim Two does not have the humidity sensor, but there is a black box around the rear view mirror like this. No exposed wires.

 

What "exposed wires" are people talking about?
I got the same box.
Why do I need a box to "detect fog on the windshield"? I can see it!
And if it does detect any humidity, then what happens?
My box doesn't do anything. Or activate anything.

Just another Prius gimmick.

 

See the image on the first post. You see wires from the roof plugging into a black box near the rear view mirror.

 

I believe if it senses humidity, it is supposed to direct air up to the windshield to clear it. My car does not have that sensor, though.

 

Mine doesn't have any exposed wires. It says in the Manual that it "Controls the Air Conditioning System to prevent fog"

 

That looks a lot like the box on my 2017 Trim Two without the sensor.

 

There are a few wires embedded on the surface of the windscreen the opposite side of the humidity/wiper sensor which I'm intrigued by:

They look like those used in a heated rear-window.

BUT unusually, one of them (RH) joins to nothing - so it's not part of the circuit - any idea?