I thought that I was buying a quality vehicle that had adaptive cruise control, but I find that the cruise control does not work on the 200UX as I expected.
The thing works well if it is on and you approach a vehicle from behind that is slower that you, it slows down, even to the extent of applying brakes. All good so far.
However, if you do not have a vehicle in front and come to a gentle down hill, the speed can exceed the set point. A warning beeper goes off to tell you that you are over the set point. Big deal!
However if the hill is slightly steeper, the speed increases to at least 5kph over the set point and finally the thing decides to do something about it. It corrects, not by applying the brakes but by suddenly changing gears (probably into 2nd or 3rd from 9th) which causes the engine to over rev. Peaks of 4,500 rpm are common, followed by a roaring noise from the engine. REALLY!
Why doesn't it apply the brakes as it does with a too close vehicle in front?
It is not good to over rev a piston engine with no load on the pistons.
The only way to stop this is to apply the brakes yourself and that turns off cruise control. At the bottom of the hill, you turn it all on again. Brilliant!
I thought I could help the poor thing along by manually changing down gradually through the gears as the speed exceeded the set point. However surprise, surprise,
the cruise control turns off when you change from auto to manual. WHY?
So when traversing an undulating road, you are continually turning cruise control on and off. Very disappointing Lexus!
Why, when it will auto brake, does this not happen with over speed down hills?
This feature is standard on Hyundai and Subaru that I know of. They maintain speed down hills by braking without turning cruise control off.

Another thing, the cruise control buttons are smooth with no pimples on them.
To make changes in speed, you have to look down at the buttons. Now I know you will get used to it, but pimples on the buttons would help you to find the right button without taking your eyes off the road.
Take a look at other brand cars and see what they are doing.
I am so disappointed with the cruise control on the Lexus 200UX that I am very sorry that I bought the car and would not recommend it to anyone else.
One final beef… the electric folding side mirrors only fold in or out with power on to the car.
It should be able to fold them back up after turning the engine off, as is the case with Hyundai.
Honestly Lexus, I expected better than this.

 

To be fair, I can understand your gripes, but for an entry level Lexus, I would say our price points have been fair and it'll never measure to to let's say the LS460 I had.

However, these are just my thoughts and just simply my opinions:

1. The cruise control 'issue', I'm not sure if it's just sensors that make it 'faulty' for you, but honestly I don't rely on cruise control that much - so it could just be a different thing for me; I like to full control of my vehicles and I am pretty 'analog' when it comes to stuff like that. Elevation/the grade of how the vehicle is going up/down while using this feature, could also cause different scenarios on how the auto-cruise is being affected.
2. A lot of cars do (and do not) have electronic folding mirrors at both a lower and higher price point; to me it's not necessary as it's just another thing that can and will go wrong down the road, they are not cheap to fix nor replace. I had them on a few of my prior vehicles and quite honestly, it didn't do much for me - what I WOULD prefer actually is the auto-down tilt when you shift into reverse so you can see a bit better when let's say parallel parking.

for a mid to high 30-k car, I would say this isn't a knock on Lexus, the UX still does plenty. The UX has awesome areas that it shines in as well. I'm hoping you will come to learn to appreciate the UX in due time; I've owned many vehicles in my lifetime and to date, the UX is still one of my favorites; but again we may have different wants and needs in a vehicle.

Best of luck.

 

I think what you are saying OP is why doesn't the cruise control apply the brakes instead of downshifting to shed off speed. I am guessing this is done (like most other cars) so the brakes don't become overburdened, and thus overheated. That would be a massive liability on the manufacturer if their cruise control algorithm overheated the brakes when the driver then needed it once he approached his exit after a long downhill, experiencing brake failure and causing an accident.

The engine "revving" to downshift isn't really affecting anything.

 

I think you missed the point. It doesn't matter whether the car applies the brakes on a down hill to stop overspeeding, or the driver does it. It still uses the brakes. Brakes are less expensive to fix than engines or transmissions.
Have a drive of a Subaru and see how well the cruise control works on downhills.

 

You're missing the point a bit. What @E46CT said makes perfect sense.

If you have cruise control set and are going down a steep hill, if the cruise control programming is designed to preserve the engine/transmission by applying braking pressure the entire way down, you are looking at a few potential situations depending on how long and how steep that hill is:

1. Your brake fluid will begin to heat up and cook and you will be left with no braking power.
2. Your pads and rotors will heat up and cause brake fade and you will be left with no braking power.
3. Your brake fluid, pads & rotors all heat up too much and you will be left with no braking power.

By downshifting, the car is able to maintain speed, even downhill, without using the physical brakes at all, all thanks to engine braking. But don't worry, your pistons will be just fine. You cannot and will not overrev your UX, nor will it overrev itself.

 

This is correct. It doesn’t matter if the pistons have a load or not, as long as the engine speed is below the rev limit, it will be ok. With a modern automatic, you cannot overspeed the engine by downshifting, the computer will not allow the transmission to go in a gear that is low enough to cause problems. Any car with a manual transmission can be over revved by downshifting too far but that doesn’t apply to the UX. All cars that I’ve had with an automatic will go above the cruise control set speed while going downhill. Some will exceed the set speed more than others. What I normally do, as I start down the hill, I’ll set the selected cruise control speed lower, this results in the transmission to shift down sooner and control the speed better. At the bottom of the hill, I’ll reset the CC back to the speed I want to cruise at.

 

Is this your first automobile with Cruise Control? I’ve own many cars over the years and they all slow the car down that way (on declines). My Lexus RX did it, my NX did, UX does it, as well as non-Toyota/Lexus brands. As the others have said, it’s a safety related.

 

Thanks for the reply.
I've had two other cars with cruise control but not with "intelligent" or adaptive.
I test drove two other brands recently and they both applied the brakes to maintain speed without a vehicle in front causing the slow down. I assumed that the Lexus would be smart enough to do the same.
It's not a safety issue, because you would have to be insane to use CC on a very long, very steep hill. In that case you turn it off , gear down and use minuimum brakes.
This is for highway cruising with the usual ups and downs without having to fiddle with the CC buttons.
I am very happy with the car in general but very disappointed with the CC and am thinking of getting rid of it. Any offers? I'm in Sydney Australia.
The way it slows down is appaling. It leaves it much too late to start correcting and then over revs it.

 

It does this in my 2019 250h. The mirror control switch has to be in either Left or Right, not in the middle.

 

I believe that's if you have the Premium package.

 

What happens if you start lowering your set speed a little bit? Does it start to apply brakes then? My GS will brake pretty aggressively if I quickly reduce the set cruise speed.

 

When driving in dynamic cruise and when approaching a slowing car ahead, my 2024 lexus es300h continues to speed at the set cruising speed. I have to apply brakes to avoid a crash.