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I have a 2016 RAV4 Limited Hybrid which I bought in September 2016 and which has worked flawlessly up to this point. But today, I was driving from Washington DC to New Jersey mostly on I-95 and the Pennsylvania Turnpike, total travel time about 4 hours, temperatures in the upper 30's to low 40's, light to moderate rain, but NO snow or ice. About 75 miles into the trip, while doing about 70 mph on I-95 in Maryland, the adaptive cruise control suddenly failed while it was in use, and a warning light and message came on that the pre-collision warning system was "not available." At the same time, the navigation system told me to "make a U-turn." I could see that the screen on the nav system was clearly totally lost in some other part of Maryland; apparently the GPS was in never-never land.

After about 30 miles, with the navigation system still in Blair-Witch country in Maryland and the adaptive cruise control unavailable, I pulled off at a rest stop, turned the engine and electrical system completely off, and then restarted the car. At that point, the navigation system "refound" itself on I-95 and worked fine for the duration of the trip home. The pre-collision warning system, however, remained unavailable, along with the adaptive cruise control, until about 20 miles from home after the rain had mostly subsided. At that point, I noticed that the pre-collision warning system warning light was no longer lit, and I was able to engage the adaptive cruise control normally.

Since I am new to RAV4's, has anyone heard of a situation in which the pre-collision warning system and the navigation system would fail simultaneously? Is there a link between the 2 systems or is this just an improbably coincidence? If the navigation system and the cruise control/collision warning system are unreliable in the rain, that seems like a major flaw, since that is when you are most likely to need all the technological help that you can get.

Many thanks to all.
 

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Read section 4-5. Using the driving support systems of the manual, moderate rain can effect the cruise, particularly at higher speeds. Dunno about the Navi issue, but Entune systems have a lot of bugs, there's a current(Dec '16) dealer installed TSB update that supposed to fix a lot of issues.
 

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I've always heard that you should NEVER use cruise control in the rain or on any slick roadway.
 

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FWIW, you can reboot the nav and audio system while driving just by holding down the power button. Its not uncommon for it to lose its way if the sat signal drops out. Weather can certainly cause that.
As for the radar, it doesn't take ice or snow to interfere, if the air itself is full of rain the radar won't work.
 

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I spent many years of my career working on microwave communications equipment (microwave radio systems) before it was replaced with fiber optic transmission equipment. In the far northern regions of Ontario where it is impractical to install fiber, microwave transmission towers are still functioning.

Microwaves ( which really mean radio frequencies in the gHz range) are affected by water. You can see how water absorbs the microwave energy everyday in your microwave oven. Without this "law of physics" microwave ovens would not heat food.

If you happen to be a subscriber to satellite television, you have probably seen your TV signal disappear during heavy rains. Also note that the rain doesn't have to be in your immediate location, but if it is anywhere between you and the satellite, reception can be reduced. As a result this phenomenon becomes more noticeable when getting television signals from a satellite over the equator than getting navigation signals from an overhead satellite.

The interesting thing is that although water blocks/absorbs microwave energy, frozen water (i.e. ice) has no effect on microwaves and allows them to pass unobstructed.

Since your adaptive cruise control uses radar (operating in the "microwave" spectrum), as well as the satellites used in the GPS system, it is completely normal for both of them to be affected by heavy rains. There is nothing for you to be concerned about, but be aware these systems may be unreliable during these conditions.

Now having said that, my somewhat advanced experience with GPS has been that it would take a torrential downpour to have much effect. I have had only limited experience with ACC (adaptive cruise control) , so I can't comment on how heavy the rain will have to be to affect that system.
 

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...and add that whether it is actively raining (heavy or not) or the rain has recently passed, the danger remains. I would imagine that the road spray from cars ahead would make it difficult/impossible for our ACC to adequately "read" the relative acceleration / deceleration of the car in front... Who in their right mind would tempt that fate? Even on a clear af day, I won't rely on ACC. Driving a car is a full-attention endeavor and ACC is tool that (IMHO) opens the door for a lazy mind and disengaged driving.
 

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ACC if used right reduces driver workload an fatigue.

It also keeps a healthy distance to vehicles in front giving you better chances to avoid problems.



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I respectfully submit to the forum that if the positive impact of the ACC on driver's (the brains behind the wheel) workload and fatigue is appreciable, and the ACC is a better judge of safe driving distance than said brains behind the wheel, then said brain should probably best get off the road, and allow others safe travel.
 

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If anyone is interested I had the ACC and the pre-collision to disengage two times;

1 driving in light snowfall where suddently i noticed that the ACC approaches car in front and without me tapping the brake pedal it would have bumped into it. Momenta later I got a clean the sensor message. Cause was thin thin ice buildup like micro layers on the sensor.

2 driving in heavy rain got message that pre-collision cannot be used. Then followed by clean sensor message. Cause: dirty sensor
This was more of an experiment I noticed the car symbol go in and out at (it indicates if it has a "lock" on vehicle ahead).


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Ours sat overnight in freezing rain recently and the parking sensors gave an error message the next morning. As soon as the ice melted, everything was fine.
 

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I respectfully submit to the forum that if the positive impact of the ACC on driver's (the brains behind the wheel) workload and fatigue is appreciable, and the ACC is a better judge of safe driving distance than said brains behind the wheel, then said brain should probably best get off the road, and allow others safe travel.
only when it's snowing or raining?
 

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Ours sat overnight in freezing rain recently and the parking sensors gave an error message the next morning. As soon as the ice melted, everything was fine.
Just to clarify for anyone reading this, the thread has been focused on the adaptive cruise control which uses radar ( which uses radio frequencies in the microwave band). The parking sensors use ultrasound to detect nearby objects.

Radar should only be affected by water and not ice, whereas an ice buildup on the parking sensors will block ultrasound.
 

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Just to clarify for anyone reading this, the thread has been focused on the adaptive cruise control which uses radar ( which uses radio frequencies in the microwave band)...Radar should only be affected by water and not ice...
How can radar be affected by water but not ice?
 

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How can radar be affected by water but not ice?
So, keeping in mind that Radar uses microwaves, any reference to microwaves is also relevant to Radar.

I took a moment to Google your query, and here are the first few results. Some of them aren't the best written articles in the world, but if you want to spend the time, you can call my Uncle Google for further information.
#1, #2, #3

This PDF file is specifically about automotive radar, and confirms what whas said in the previous references regarding Microwaves.
 

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Read my post #11 about ice build on the radar sensor, i had a few mm of ice and it affected the radar. There was no dirt you could eat from the surface just ice.


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Read my post #11 about ice build on the radar sensor, i had a few mm of ice and it affected the radar. There was no dirt you could eat from the surface just ice.
driving in light snowfall where suddently i noticed that the ACC approaches car in front and without me tapping the brake pedal it would have bumped into it. Momenta later I got a clean the sensor message. Cause was thin thin ice buildup like micro layers on the sensor
I have no doubt that you experienced a problem during a snowfall. I'm just not totally clear on what lead you to your conclusion that it was caused by ice buildup.

From what I understand, you were driving in a snowfall and you received the "clean the sensor" message and you didn't find any dirt, only ice on the sensor. It's not clear if you wiped the sensor off and eliminated the problem immediately by doing so.

I believe it is more likely that the falling snow caused the "clean the sensor" message and what you found on the sensor (layer of ice) had nothing to do with the message. Because the ice was the only obstruction (i.e. "dirt") that you found, you assumed it was the cause of the problem.

Regardless, the laws of physics explain that microwaves are not absorbed by ice in the same way as they are in water. I experienced this first hand when I was working as a technician on microwave radio transmitters. The wave-guide that carries the signals was normally kept pressurized so that water could not enter. Occasionally a leak would develop and the water that seeped in would collect in low spots and totally block the reception of the radio signal. If we couldn't get to the location before nightfall, the radio often started working normally again as the water turned to ice.

In the environment that a car lives in, it would be difficult to get ice without water being present as well, so it becomes more difficult to determine the real cause of the microwave signal fade that you experienced. Also keep in mind that if you run water over the front of your car while washing it, there will probably be no affect at all on the operation of the ACC. It will take a lot of water (like a rainfall or a wet snowfall) to cause a problem.

So I'm not saying that you didn't experience a problem, but both the laws of physics, and personal experience, say that ice will not block microwaves, and your problem was more likely to have been caused by the water molecules in the snowfall.

By the way, I have been using ACC on my current vehicle (not a RAV4) for 20 months now, and have only experienced very brief instances of a problem when driving in rain and snow. So apparently it takes some pretty heavy rain/snowfall to knock out the system for more than a few seconds at a time.
 

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I stopped at a gas station to check it out but decided just to go home. The next day it was warmer weather so the ice layer was gone and the system worked well again. But there was no more snow that day so you are perhaps right.

Thanks for the clarification.


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14694/Final_Papers/GM0022-F.pdf"]This PDF[/URL] file is specifically about automotive radar, and confirms what what said in the previous references regarding Microwaves.
The conclusion in the PDF states: "Dielectric material, like ice layer with its negligible absorption coefficient, exerts generally less influence on the performance of automotive radar sensor."

It says less influence, not no influence. I will agree that water is (perhaps much) worse than ice in terms of reducing the radar effectiveness.
 
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