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Ok I am going to be serious... I promise @Sarang. Putting aside the ceramic hypothesis for a minute (I just don't want to go there...), the detection system will stop operating when some of the following occur: thick snow around the sensor area; the temperature around the sensor becomes too high/low; or when the vehicle battery voltage becomes too high/low. Or if your car is lifted off the ground and the wheels are freely turning. So I have no idea of what the sister-in-law was doing at the time the little amber light was not on (but should have been), or the environment she was driving in, but it is possible the voltage was low or the temp was too high etc (noting is is summer in the northern hemisphere) and the ECU switched it off then she stopped the car and called in a panic. Then the OP gave her the David Copperfield option and she did the Karate Kid Daniel San wax on wax off wipe. Then got back in the car turned it on and went for a drive and it worked. Then she became ecstatic. Why did it work? Because the sensor had cooled down or the sensor is out of a direct line of sight to the hot sun or the voltage is more normalised due to a number of factors (most likely change in load or the battery had charged up above the cut-off threshold).

Also, it is also possible the sister-in-law hit the switch that turns the sensor off. But I have ruled that out because, unlike Start/Stop where it resets to on after the car restarts, the sensor switch remembers the last state. So if she hit the switch to turn it off then she would have had to also hit the switch to turn it back on. So very unlikely to accidentally hit the switch twice to turn it off then on at specific times.

I also have a grassy knoll theory, but that involves a second ceramic sprayer....
 

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2022 Canadian Sport trim (6MT // 2.0 )
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Let's get dirty. Subaru uses a 24 GHz system [1] (blind spot, rear cross-traffic alert etc). It's designed to function with an appropriate power margin in mist/rain/sleet/snow and with a wet bumper, so a little bit of water isn't an issue. The so-called "ceramic" coatings are basically SiO2 suspended in a polymer. K-band properties of polymers ..well they really depend on polymers., while fused silica is a dielectric for radar waves, so it shouldn't cause problems.

One hypothesis is that the sprayed-on layer screwed up the propagation of the signal near the transceiver. Looking at referece [2], there are two interesting pieces of information
  • a 15 dB loss at 24 GHz for a 0.5 mm water film (which is quite large, but since it's just attentuation, it could still be within the operating margin of the system)
  • a -2 dB reflectivity from the same water film. This could imply that the reflected radar signal (especially that the film is nearly on the sensor) is strong enough to overwhelm the signal reflected from the obstacles (which is attentuated), and cause the system to be inoperative. Think of it as being dazzled by a flashlight's reflection from a tinted window.

[1] MSA5P1926C.pdf (oemdtc.com)
[2] download (psu.edu)

Bottom line, it is possible that the spray-on detailing solution which was meticulously applied onto the bumper did end up interfering with the radar sensor. Not enough evidence to say it did for sure, but it seems indeed that the hypothesis cannot be ruled out.
 

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2021 Subaru Crosstrek Limited
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548 Posts
Let's get dirty. Subaru uses a 24 GHz system [1] (blind spot, rear cross-traffic alert etc). It's designed to function with an appropriate power margin in mist/rain/sleet/snow and with a wet bumper, so a little bit of water isn't an issue. The so-called "ceramic" coatings are basically SiO2 suspended in a polymer. K-band properties of polymers ..well they really depend on polymers., while fused silica is a dielectric for radar waves, so it shouldn't cause problems.

One hypothesis is that the sprayed-on layer screwed up the propagation of the signal near the transceiver. Looking at referece [2], there are two interesting pieces of information
  • a 15 dB loss at 24 GHz for a 0.5 mm water film (which is quite large, but since it's just attentuation, it could still be within the operating margin of the system)
  • a -2 dB reflectivity from the same water film. This could imply that the reflected radar signal (especially that the film is nearly on the sensor) is strong enough to overwhelm the signal reflected from the obstacles (which is attentuated), and cause the system to be inoperative. Think of it as being dazzled by a flashlight's reflection from a tinted window.

[1] MSA5P1926C.pdf (oemdtc.com)
[2] download (psu.edu)

Bottom line, it is possible that the spray-on detailing solution which was meticulously applied onto the bumper did end up interfering with the radar sensor. Not enough evidence to say it did for sure, but it seems indeed that the hypothesis cannot be ruled out.
While it may be remotely possible for the ceramic to cause interference, simply wiping it with a wet rag will not remove the SiO2/Polymer. That has been my point all along.

There are tens of thousands (if not more) of cars with a ceramic coating, ceramic spray on coating, or a hybrid/wax combo. If it were even remotely possible, this wouldn't be the first time anyone heard of it. It would have been mentioned years ago when these coatings started coming out.
 

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2022 Canadian Sport trim (6MT // 2.0 )
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That's the major counterargument. There should be posts all across automotive forums, since the 24 GHz is widespread, as is obsessive car detailing with a bazillion of products.
It might not be the product itself - but the weatherproofing and design of sensor casings themselves. Anecdotal evidence, but a high-pressure wash disabled the same sensors on a friend's mercedes. So maybe, sometimes, if a drop of something gets somewhere.. it fails.

The best way to settle this would be for the OP has to meticulously re-create the original event 5 times to get some consistency in data, and then vary 1 variable at a time. Including replacing his sister-in-law by another subject😁
 

· Resident topic drifter
'18 and '19 Crosstrek Limiteds
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17,759 Posts
As said before, the OP has to meticulously re-create the original event 5 times to get some consistency in data, and then vary 1 variable at a time. Including replacing his sister-in-law by another subject😁
You think the OP is going to come back now? 😸
 

· Resident topic drifter
'18 and '19 Crosstrek Limiteds
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17,759 Posts
I dunno. He seemed to go away mad. 🤷‍♂️

Hope it wasn't something I said. :devilish:
LOL, just to clarify my first comment, though, I did find it odd that the OP signed up just to post about this, without any real evidence. Usually, first posts are a question or complaint about something, or an introduction with a new car, sometimes with pics. To me, this one was odd...
 

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LOL, just to clarify my first comment, though, I did find it odd that the OP signed up just to post about this, without any real evidence. Usually, first posts are a question or complaint about something, or an introduction with a new car, sometimes with pics. To me, this one was odd...
And he posted the exact same post on another thread.
 

· Resident topic drifter
'18 and '19 Crosstrek Limiteds
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17,759 Posts
Meh. It seems like he posted an issue and solve for it that he thought was worthy of sharing, and when it didn't receive the reception he wanted, he backed off. Not that strange really.
What I meant by "odd"

Someone signs up here for the sole purpose of promoting something like that?

Not what I've seen.
 

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Let's get dirty. Subaru uses a 24 GHz system [1] (blind spot, rear cross-traffic alert etc). It's designed to function with an appropriate power margin in mist/rain/sleet/snow and with a wet bumper, so a little bit of water isn't an issue. The so-called "ceramic" coatings are basically SiO2 suspended in a polymer. K-band properties of polymers ..well they really depend on polymers., while fused silica is a dielectric for radar waves, so it shouldn't cause problems.

One hypothesis is that the sprayed-on layer screwed up the propagation of the signal near the transceiver. Looking at referece [2], there are two interesting pieces of information
  • a 15 dB loss at 24 GHz for a 0.5 mm water film (which is quite large, but since it's just attentuation, it could still be within the operating margin of the system)
  • a -2 dB reflectivity from the same water film. This could imply that the reflected radar signal (especially that the film is nearly on the sensor) is strong enough to overwhelm the signal reflected from the obstacles (which is attentuated), and cause the system to be inoperative. Think of it as being dazzled by a flashlight's reflection from a tinted window.

[1] MSA5P1926C.pdf (oemdtc.com)
[2] download (psu.edu)

Bottom line, it is possible that the spray-on detailing solution which was meticulously applied onto the bumper did end up interfering with the radar sensor. Not enough evidence to say it did for sure, but it seems indeed that the hypothesis cannot be ruled out.
I am having trouble with my BSD system and rear sensor not working. The car was in an accident. How can I find the technical repair manuals like you listed for this other vehicle for my 2017 Subaru Crosstrek . Thanks
 

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2021 Crosstrek Limited
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2,776 Posts
My #4 post shows how to recalibrate it.
 
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