Adaptive Cruise Control malfunction

[BobbyR]

We were driving on an expressway a few days ago travelling at about 70 MPH in the right hand lane. As we approached an exit ramp the car in front of us signalled to exit and started slowing down to enter the ramp and leave the expressway. He exited normally and slowed down quickly to about 40mph. To my surprise, my car braked suddenly, apparently still tracking the exiting vehicle. This has never happened before and took me completely by surprise as the car was no longer in front of me and was therefore no longer of interest. Fortunately there was no one behind me as I fumbled to regain control of the vehicle. This may not sound like a big deal but, take my word for it, when your car brakes suddenly for no apparent reason at 70 mph it is a very unsettling experience. I don't even remember what I did to regain control. This was a dangerous malfunction of the system and I am now reluctant to use adaptive cruise knowing this sort of thing can happen. Anyone else have this happen to them? For those who haven't, be aware.

[TwoTone]

I love these posts.

[SubieN8]

I am thankful to work at home.

[laz]

You should always be in control of your car.

[thefultonhow]

I don't even remember what I did to regain control.

 

It probably had something to do with hitting the accelerator pedal.

 

How is it so hard to "regain control" from your car braking? Is this the pussification of Subaru? I remember quite a few times in my 05 LGT where I floored it and the tail came out. God forbid that kind of thing ever happens to you.

 

This was a dangerous malfunction of the system and I am now reluctant to use adaptive cruise knowing this sort of thing can happen.

 

So don't use it. Sounds like that's the best idea for everyone involved here.

 

Oh, also, the adaptive cruise in my mom's Tesla brakes for overpasses on a semi-regular basis. At least your car was braking for an actual other car.

[wi_legacy2016]

My advice is next time you're in that situation, keep an eye on the gauge cluster and if the indicator that your car is tracking the other car doesn't disappear in a timely fashion, just turn off the cruise control momentarily and then resume after you've passed the exit.

 

The other thing that might help is if you were using the closest following distance, to use a further following distance setting. For interstate driving, I use one of the middle settings (2 or 3).

 

It's not a self-driving car so you need to pay attention. I don't think that means ACC is not useful for longer drives overall. Looks like you have a 2018 so you're probably newer to using it. Over time you'll learn scenarios where it's likely to do something a little goofy.

[laz]

I say you return it and get a no frills Kia.

[Yoda_One]

@BobbyR You need to take sometime out for your busy life to read the Warnings using Automatic Cruise Control in your Eyesight Owner's Manual. It should put you in perspective about the short comings, then read how tos. I very rarely use ACC unless I am on a long expressway trip mainly as I would have use standard CC. It is not needed for Eyesight to function to its potential, it is a great driver assistance for handling drivers fatigue and drivers strain when used within it's limitations.

[tumbleweed 49]

This is fairly common with ACC or radar cruise control systems, my Toyota would do the same thing. The cruise control can't tell when the car in front has turned and is proceeding off the road, it just sees something blocking the road in your lane and brakes to avoid it, it doesn't detect the perpendicular motion of the car moving off the road.

 

The solution is to be aware it will happen and push on the gas pedal to override it. It is a quick easy reaction and with a little practice it will become automatic.

[ammcinnis]

This was a dangerous malfunction of the system ...

There was no malfunction in the scenario you describe. Don't blame EyeSight for your inattention. EyeSight (including ACC) is a driver-assist system, not an autopilot.

[laz]

There was no malfunction. Don't blame EyeSight for your inattention. EyeSight (including ACC) is a driver-assist system, not an autopilot.

 

But how can you text while the car is suddenly stopping for no good reason?

[upstater]

I use ACC all the time, even around town (in total violation of the Owners Manual!)

 

It sometimes over-reacts to vehicles that are turning as it cannot judge when they will clear the lane. Very predictable, not actually outside of the parameters of how ACC works.

 

I like stop/start ACC, I will only buy cars with it now. If and when I don't want to use it, I just don't turn it on.

 

Lotta haters here, personally, I don't care if you like or hate these safety features, the more people that end up with them (I would guess they will be required eventually, just before self driving cars become a thing) the safer it is for everyone, it might stop someone from rear ending you -- unless you like the idea of an inattentive driver or slow reacting senior citizen rear ending you (which even the best driver has zero control over).

[BobbyR]

I understand the skepticism in many of these responses and I anticipated them when posting. I would probably have responded the same way had this not actually happened to me. All I can say is that I have been using this system since getting the car and am familiar with how it works and have had no issues with it until now. I was in control of the car and attentive to the traffic around me and the overall situation. I was not relying on the system to drive the car for me. I was relying on it to work as advertised, maintaining my speed and/or spacing behind the traffic in front of me. I am a good driver.

 

The post was intended to warn those reading it to be aware that this system has some serious surprises lurking in its AI brain and they aren't all good. Trust me on this. If it happens to you you will not like it.

 

Enough said.

[laz]

Just thank your lucky stars that you did not have to deal with the first version of eyesight. No system is perfect but it will get better.

[XT-sub]

... my car braked suddenly, apparently still tracking the exiting vehicle. ...

...

... Anyone else have this happen to them? ...

 

Yes, something very similar has happened to me a few times with both model EyeSight equipped Subarus (our earlier Foz SJ XT & current Liberty 3.6R). Quickly applying throttle to override EyeSight when using ACC in that situation is the workaround that I use.

 

The braking & turning vehicle is still in EyeSight’s field of view, so it is doing what it was designed to do. But because the other vehicle has already moved to another lane & EyeSight is still quite severely applying the brakes, I’m sure Eyesight could do with some fine tuning for this situation.

 

Subaru Australia have known about this shortcoming for quite a while (I reported it a couple of times when I had the SJ Foz XT), so I’m guessing Subaru in Japan who design the cars would also know. Hopefully they will fix or improve it in the next version of EyeSight.

 

The concern that I have with the above situation when travelling on the highway at around 100 km/h; is if a following vehicle (especially a heavy truck) is close & doesn’t react quick enough to my vehicle’s sudden severe braking, & if I don’t get on the throttle quick enough, there is the possibility that it could cause an accident.

[Back Road Runner]

The way the adaptive cruise works is it's looking for anything within the entirety of your lane. Even as cars enter or leave, as long as they are a tiny bit in the lane, they're in the lane. This unfortunately means as cars leave your lane and brake, it will brake with that car even though it's exiting the lane and should be out of your path by the time you'd be in that space. The adaptive cruise is not predictive in this sense. It just deals with what's in front of you, any part of the area in front of you.

 

Is it annoying? Sure, but it's not really a big deal. If you want to have it happen less, run a closer distance setting. setting of 1 or 2 is much less influenced by this and is relatively aggressively close to the cars in front of you where it doesn't feel weird to have it slow with the very close car in front of you. It's only in the longer distance settings of 3 or 4 where to you the car is sufficiently away that you anticipate it leaving your lane well before your car gets to that location. The Eyesight system doesn't do this so all it does is try and maintain that long distance, even though the car is leaving and slowing way down. It sees the slow down and brakes for you.

 

Should the Eyesight system be more intuitive? Sure. Eventually it likely will be reading cars coming into and out of the lane and monitor areas around the car for additional options for crash avoidance if braking along isn't sufficient. This may be future programming some years down the road and likely much closer to autonomous driving too.

 

Was it a bad idea for Subaru to not differentiate cars in, leaving, and entering the lanes? Kind of. One critical benefit that this annoying function offers is it will protect you in your lane if cars are barely in your lane (either coming in or not quite leaving the lane). This works quite well for your protection with you or other cars entering and exiting lanes. Basically, it protects against offset crashes which is certainly good. Your benefit as a human is more so seen at the lower settings or when you have cruise control off and it's simply performing emergency crash avoidance. Either way, the system's doing the same thing. It's just doing it closer and closer and more aggressively braking as you step down in distances and through emergency collision detection.

 

Now one interesting note is the new Ascent has some more advanced adjustments that does let you tune this behavior more. It's an indicator that Subaru recognizes that people want a little flexibility in how the Eyesight follows traffic, brakes, and accelerates. I don't believe it has any monitoring of cars moving in and out of lane and making adjustments to that, but it at least is offering some more flexibility in how it behaves.

[XT-sub]

The way the adaptive cruise works is it's looking for anything within the entirety of your lane. ...

 

Yes, I understand how ACC works, but in the handful of situations in over 5 years that I am talking about it doesn’t work anywhere near as smoothly every time as it should.

 

At slower speeds such as 50km/h to 80km/h it isn’t an issue, but at 100 to 110km/h it is. At the higher speeds the delay is too long before Eyesight reacts to the braking vehicle leaving the lane & therefore very aggressively applies the brakes. I could react quicker than it does, but when it does eventually react, the brakes are applied that hard it almost stands the vehicle on its nose. And when the turning vehicle has fully moved out of my lane, my vehicle takes far too long to stop applying the brakes. That is my experience with both EyeSight equipped Subarus.

 

Subaru Australia suggested to use either ACC’s 2nd or 3rd distance marker & not to use the closer 1st distance marker on the highway. I found that doing this does reduce the number of incidents, but doesn’t eliminate all.

 

Is it annoying? Sure, but it's not really a big deal. ...

It could be a big deal, see the last paragraph in my previous post.

[ammcinnis]

I was not relying on the system to drive the car for me. I was relying on it to work as advertised ...

Unrealistic expectations. Expecting system behavior contrary to what is documented in the Owners Manual (i.e. behavior "as advertised") does not constitude a product deficiency.

[ammcinnis]

The way the adaptive cruise works is it's looking for anything within the entirety of your lane. Even as cars enter or leave, as long as they are a tiny bit in the lane, they're in the lane. This unfortunately means as cars leave your lane and brake, it will brake with that car even though it's exiting the lane and should be out of your path by the time you'd be in that space.

Correct ... with an emphasis on "should be out of your path." Your driving experience may tell you that the leading vehicle should be out of your lane by the time you get there, but that's still not a guarantee that it will be. EyeSight is programmed conservatively: until a vehicle has totally vacated your lane it is considered to be a potential obstacle.

 

Anecdotally, I recently encountered a scenario like this, in which EyeSight was right and I was wrong: While cruising with ACC engaged, the vehicle in front of me signaled a right turn and began slowing, and I applied light throttle to maintain speed and avoid braking. Then, inexplicably, the lead car stopped abruptly, midway through the turn, blocking the right half of my lane. If there had been a vehicle next to me in the left lane I might not have been able to steer around the lead car and avoid a collision. In this case, EyeSight was right; my experience and judgment was wrong.

[upstater]

I avoided a rear end collision with Eyesight (not ACC) because the driver in front of me turning right onto an onramp decided at 30mph to slam on her brakes to give the right of way to a car that was turning left across two lanes of traffic to merge onto the onramp (that car was slowing to provide for the right of way, not that she noticed).

 

She was smoking her tires sliding, my car braked at 100% and there was no collision.

 

There are a lot of terrible drivers who do stupid unpredictable things, which explains why I stopped riding motorcycles.

[midas]

I used ACC for 3 years on my 2015 Sonata. Where the Legacy relies on cameras for it's system, the Sonata was all radar. Both systems have the same limitations as described in this thread. The Legacy system is a little better, but not by much.

[ehsnils]

I predict that future systems will use both cameras and radar. It's a very immature technology that don't "understand" all special cases. Rotaries are fun with the Eyesight system - and we have a huge number of rotaries here.

[Brisvegas]

Rotaries are fun with the Eyesight system - and we have a huge number of rotaries here.

 

That post had me a bit confused until I did some Googling

 

At first I thought why does having having a lot of Rotary clubs near you, affect the Eyesight system? But I have since discovered you are probably referring to "roundabouts."

[coldsoda]

That post had me a bit confused until I did some Googling

 

At first I thought why does having having a lot of Rotary clubs near you, affect the Eyesight system? But I have since discovered you are probably referring to "roundabouts."

 

And I was thinking he was talking about Mazda having eyesight... rotary is not a term I've heard in the midwest or now in AZ, LOL

[upstater]

I predict that future systems will use both cameras and radar. It's a very immature technology that don't "understand" all special cases. Rotaries are fun with the Eyesight system - and we have a huge number of rotaries here.

 

we have rotaries here, never had an eyesight issue in them.

 

the main 'auto braking' issue its when a car is slowly exiting the lane, where most drivers might slow a bit then swerve around the car, eyesight sometimes acts like they are parked in the lane (OP's issue).