Cruise control accelerates downhill

On my 2011 Legacy with CVT, the cruise control will hold speed downhill about 10% of the time, and will accelerate all other times. In fact, the car will stay closer to cruising speed if the cruise control is disengaged at the top of a hill and re-engaged at the bottom. Subaru states that this operation is normal, when my last Legacy (a 2005) and my wife's Impreza (a 2013) will hold speed downhill. Any one else with this problem? If Subaru will not fix, I intend to go to the National Highway and Traffic Administration to report a dangerous defect and request a recall. I live in a mountainous area, and there is no point to cruise control if its operation needs to be constantly and closely monitored.

Mine feels like I lose control anytime going downhill. Its quite unnerving. It accelerates past the speed set and then settles off once on flat road. Def not only yours.

It sounds like you are talking about mildly steep grades? And how much "acceleration" are you talking about? Most cruise controls accel and decel within a range of a couple MPH. My co-workers 2012 2.5i doesnt seem to have this problem when driving in the Adirondacks.

What happens to the engine RPMs when the car accelerates?

If the RPMs stay constant, the CVT is shifting up for higher efficiency, if the RPMs increase the CVT is holding a gear. If may provide some clue as to what is happening. If the CVT upshifts, the engine braking power goes down and you'll accelerate. Its probably worth comparing the behavior of the CVT with and without cruise control. Once you've gotten some data, your best bet is probably to directly contact SoA. While statisfying to get the NHTSA involved, you'll probably be in a new car before they finish an investigation.

Is this also an issue with the 5EAT and 6-speed or specific to the CVT?

Do Subaru automatics have some sort of grade logic like Honda autos do? If not, then what you are see is completely normal. The fact that your other vehicles don't do this could simply be due to the larger rolling mass of the Legacy or something.

My CVT powered '12 Outback will speed up on hills and it's not because the cruise control just makes it, it's just because it's a big vehicle rolling down a hill. I paddle shift down a couple 'gears' if I don't like it and then just reengage cruise at the bottom. No big deal.

This will definitely happen with a 6spd since the driver will either need to downshift or apply the breaks to prevent the car from speeding up on steep descents.

The 2010 to 2012 CVT legacy's do not have a grade logic or hill decent control. The cruise operated like any other vehicle, if you go down hill the system does not slow you down. If it is a big enough grade hill, you can speed up quite quick. THis is like any other cruise control I have had except in my "13 outback... LOVE the eyesight

Originally Posted by eckseleven

This will definitely happen with a 6spd since the driver will either need to downshift or apply the breaks to prevent the car from speeding up on steep descents.

The CVT can exaggerate the effect if it upshifts (for efficiency) as you descend. A 6-speed would remain in the same gear with the RPM increasing and getting more engine braking. Imagine shifting 5->6 as your car picks up speed, you'll get much more speed than simply staying in 5th.

1) Why are you using cruise control on mountain hills anyway? Do you not care about fuel economy?

2) Cruise control will not apply the brakes, nor downshift, to slow the vehicle. You are expected to be "constantly and closely" monitoring the behavior of your vehicle at all times.

3) CVT's are notoriously bad at engine braking. Occasionally, you might find a spot in their logic where they will not free-wheel, but I'd bet that most of the time you think the car is accelerating it is merely freewheeling. Gravity accelerating the car, not the engine.

4) Good luck trying to get NHTSA to force Subaru into issuing a recall. There is nothing wrong with your car.

Originally Posted by EddieT

On my 2011 Legacy with CVT, the cruise control will hold speed downhill about 10% of the time, and will accelerate all other times. In fact, the car will stay closer to cruising speed if the cruise control is disengaged at the top of a hill and re-engaged at the bottom. Subaru states that this operation is normal, when my last Legacy (a 2005) and my wife's Impreza (a 2013) will hold speed downhill. Any one else with this problem? If Subaru will not fix, I intend to go to the National Highway and Traffic Administration to report a dangerous defect and request a recall. I live in a mountainous area, and there is no point to cruise control if its operation needs to be constantly and closely monitored.

I hate to insult someone on their first post, but you are what scares me on the roads.

You are why I hate all the new tech in cars. You don't want to drive you want the car too do it for you.

You are that person that when the blind spot warning system or the adaptive cruise control, or the auto braking, or lane departure warning fails -- will blame it on the car and not you utter lack of attention.

It's cruse control, you are still responsible to closely monitor what is going on with your car at all times.

/rant off

The acceleration is more than a few MPH. On a modest hill, the vehicle will quickly pick up 15 mph in my test, and continue to accelerate if permitted. The fact is that the cruise control from some other manufacturers does not behave in this manner, and there is no excuse for Subaru's use of an inferior design. In fact, Subarus are better sellers in mountainous areas, which should be a factor in the design. Furthermore, the use of cruise control invariably improves mileage. Since posting the message, the service manager at the local dealership has tested the cruise control in a few vehicles, has found the same problem, and is taking the issue up with Subaru. The ranters and trolls can keep their Michael Schumacher dreams to themselves, and they are the ones who frighten me on the road. I am not suggesting the use of cruise control on I-90 near D.C. When driving 150 miles on a divided, lightly traveled, limited access road in the Appalachians, then the use of cruise control reduces weariness as well as improving gas mileage, and it does not connote inattentiveness. If I did not immediately catch the acceleration problem, then I would not be posting on this forum; my concern is for others, including older family members, who might believe that "cruise control" actually controls the cruise. My belief is that less public acceptance of this inferior design would induce Subaru to make the improvement in future models. Get off your high horses.

Is the car accelerating because the engine is getting more gas, or is the car accelerating because it's going down a hill?

I don't know how universal this statement is, but the cruise control function is not intended to be used in hilly terrain. It's used for long stretches of flat, empty highway.

Like what BAC5.2 said, the system doesn't engage the brakes. When going down a hill, how do you suppose you will slow down? There is only so much friction and engine braking will give you.

I am not a Michael Schumacher dreamer, ranter, nor troll. If I was worried about who else might drive my car, I'd tell them not to use the cruise control feature. I would do this not because I thought the feature was broken, but rather that it wasn't meant to be used in a mountainous area in the first place.

I use my cruise control everyday, to and from work, and have zero issues with it going down hills. It may be because I have a manual transmission or maybe because I use it strictly on highways.

Same question was posted in the Outback forum, and here's a pretty good explanation from one of the members:

"...when the car coasts for a given time with no throttle input the fuel is shut off and the engine is driven by the transmission and wheels - you can feel when it happens if you pay close attention to it. You can also see the current MPG indicator peg at 99mpg when this happens.

Brakes and cruise control are not linked in anyway.

When additional engine braking is needed you can give the flippy paddle a flip and drop a gear without impacting the cruise control speed setting. The CVT is by far the most slippery drive system subaru has put in the ob so far so the engine braking ability is not as strong as other transmissions however that also translates to better fuel economy too.

I find my self using the flippy paddle to down shift the CVT on pretty much any hill which is long enough to see the car pick up speed and need more than one tap on the brake to slow it up. Leave the transmission in AT mode and the car will shift back on its own when the cruise kicks back in on the next hill climb etc."

Stop being lazy and drive your car; use your brakes and/or downshift. And as others have said, cruise control is intended for highways, not downhill mountain roads.

Originally Posted by EddieT

The acceleration is more than a few MPH. On a modest hill, the vehicle will quickly pick up 15 mph in my test, and continue to accelerate if permitted. The fact is that the cruise control from some other manufacturers does not behave in this manner, and there is no excuse for Subaru's use of an inferior design. In fact, Subarus are better sellers in mountainous areas, which should be a factor in the design. Furthermore, the use of cruise control invariably improves mileage. Since posting the message, the service manager at the local dealership has tested the cruise control in a few vehicles, has found the same problem, and is taking the issue up with Subaru. The ranters and trolls can keep their Michael Schumacher dreams to themselves, and they are the ones who frighten me on the road. I am not suggesting the use of cruise control on I-90 near D.C. When driving 150 miles on a divided, lightly traveled, limited access road in the Appalachians, then the use of cruise control reduces weariness as well as improving gas mileage, and it does not connote inattentiveness. If I did not immediately catch the acceleration problem, then I would not be posting on this forum; my concern is for others, including older family members, who might believe that "cruise control" actually controls the cruise. My belief is that less public acceptance of this inferior design would induce Subaru to make the improvement in future models. Get off your high horses.

You're the one on a high horse and woefully ignorant on operation of a vehicle.

As mentioned Cruse Control is designed to be used on long flat stretches of road not curvy mountain roads. Bet you use it in the rain also?

But please submit your complaint to NHTSA, I'm sure it will be as entertaining to read as the ones that call the Passenger Airbag lights a huge danger because of the distraction they cause or any of the other 1000's of absurd complaints.

Obviously, the users of this forum do not regard the use of cruise control as driving a car. My position remains that other manufacturers have mastered the design of cruise control for use in hilly terrain. Since you all have bought into the Subaru inferior concept that cruise control does not include any such application, I will not trouble you hot shots any further. I do not stay in echo chambers.