:mad: VSC got me in an accident today

OK, not going to beat the dead horse about ABS functionality as qbee42, Tideland and jayman got my back, there.

Just another suggestion that should help the Prius (haven't actually tested it on the Prius too many times, so practice, first! Prius seems to be better than the WRX in this regard). I first experienced the momentary lack of stopping power that ABS can incur over a briefly slick surface in my Subaru WRX.

For example, braking over railroad tracks - traction sucks over the tracks, but as soon as you get over them you have full braking power again. If you hit the brakes right before the tracks, ABS will kick in over the tracks, the pedal will go hard and you'll feel like you can't stop.

There's two things that can be done to get full braking power once you know you're on a good surface:

1. Continue to stomp on the brake with ALL your might. ABS will quickly figure out that you've got traction again and you'll stop in a hurry.
2. Briefly let off the brake and then get back on them as hard as possible (ABS should engage again if it's really a panic stop!)

I hesitate to recommend #2, as I'm sure that 99% of the time, #1 is the way to go. But sometimes letting off the brakes you can disengage ABS (which may still think you're on a slippery surface) and engage it on the good surface which can increase your braking power. It's not often this is effective as you have to be sure when you do it you're on a braking surface significantly better than the surface which induced ABS - AND you have to have room/time to let off the brake.

If this is something that affects you - you probably have some spot on the road which triggers this easily - go and see what works better for you when there's no traffic around.

 

While so much of this is true, the bolded statement is not true. With all four wheels locked up you have no steering control. The only way you'd continue in a straight line is if the center of mass of the vehicle is under no other prior force. In other words, if you lock the wheels while entering a turn, you will not simply go in a straight line on the tangent of the curve. You'll also experience the effect of the vehicle turning (one direction or the other) off of the center of the car's mass (if the tires are really providing no significant resistance).

Interesting recommendation. I believe I read in the manual that the ABS stays engaged until the brake pedal is released. If this is the case, then your suggestion may be a good way to look at the handling of this situation.

 

Get A CANBUS Monitor?

What, I like doing that.

It's your property. You should need nothing more that the desire to do so. If you want to address this, the thing to do would be to look for a CANBUS monitor that would routinely be plugged in and recording. You want to inspect an event, you just read your own data.

Anybody know of such a device?

 

By "turn" you mean spin, right? Anyway, I think you're saying the same thing that I meant, anyway, the vehicle's center of gravity will follow a straight line in a skid.

 

There are a couple of comments I'd like to make about the facts as you have reported them.

• If you were travelling at 10 MPH when the incident started you would only have travelled 15ft in the 2 seconds you say you were without brakes.
• If you allow that you only managed to decelerate at 0.25g once braking was restored (which is one heck of a slick road with badly worn tires) then it takes only 14 ft to decelerate from 10 MPH to stopped.

My point is that from applying the brakes you should only have travelled a maximum of 29ft despite the 2 seconds you say you were without brakes.

Frankly I think the problem here is that you were travelling either too fast for the conditions or too close to the car in front when it stopped unexpectedly (at least by you). You should never get into the situation where a panic stop is necessary, though we all do (including me) and this time you did not quite get away with it. So stop looking to place the blame on the car, accept some responsibility and learn from it.

 

I think you mean the Brake Assist stays engaged until the brake pedal is released. ABS may or may not be working while Brake Assist continues until the vehicle stops or the brake pedal is released.

 

I believe what was meant is that when the Prius loses traction during regenerative braking, it switches to ABS friction braking and stays in this mode until the pedal is released.

Tom

 

Precisely.

 

What Tom said.

 

Everyone should try to apply brakes mildly over railroad tracks (when it is safe to do so), and get the feeling of ABS/TCS/BrakeAssist working together in a scary way. Then, you know what to expect from modern technology.
Whenever possible and needed to do so, I apply brake BEFORE railroad tracks. Release it right BEFORE the tracks, Apply it again right AFTER the tracks. Overall, you would get a shorter stopping distance than "stomping the brake", in which case, ABS/TCS goes crazy trying to figure out what to do.

ABS shortens stopping distance in most hard surface. One loose surface, it depends. However, ABS allows you to retain control over steering, and that is invalueable in an emergency situation.

A good driver knows where the limits of his/her vehicle are.
Knowing the limits helps avoid running out of control in emergency situation.
Test the limits of your vehilces on a rainy day (or snowy day) in a wide open parking lot.
(whether it is a Prius or anything else)

 

Hi all i experienced this today and a few times in the last couple of weeks.
This is quite concerning to me because when it occurs it feels like the vehicle lurches forward half a meter to a couple of meters depending the speed i am travelling at.
I can duplicate this multiple times on a particular road i travel on a couple of times a week. Doesnt matter whether the road is wet or dry.
There is a metal strip across the road when cruising say at 60kms and i slightly apply the brakes when it the vehicle rolls over it will loose its brakes for apx half a second or just under but it does push the car forward.
I have travelled this road with other vehicles that are abs equiped and the issue is there but not as pronounced as it is in the prius.

Today i was turning into my driveway. In the middle of the road they have white square reflectors. We call them cats eyes.
Conditions where dry. As i was turning into my driveway with brakes applied not heavy the vehicle lurched forward again with the trac light flashing at me.
I think the system is over sensitive. I really hope this does not catch me out one day and i end up rear ending someone because of it.
Has anyone taken up this issue with Toyota?
If so what was there response?
Can the vehicle be reprogrammed some how to eliminate this issue or reduce it?
I know this is an old thread but thought i would revive it as this is quite concerning to me and others.
Updating the vehicle to a 2010 model is out of the question for me if they resolved this on the current model.
I will get in touch with a dealer next week when i have a moment and ask them to look into this issue. I'm hoping there is some sort of fix.
If someone could shed some more light on this it would be great.
Vehicle is a 2008 Itech (Aus Version)
Regards

 

If the yellow skid light flashes but you're not hearing beeps, you're NOT hitting VSC but rather traction control is being triggered. You're likely hitting the so called "brake pause" which IMHO (and that of most 2nd gen owners) isn't severe and isn't really a lurch forward. Repeat it a bunch of times to prove it to yourself.

I and others have submitted known locations of this on the 2nd gen. See my submission at http://priuschat.com/forums/gen-iii...99-poll-prius-brakes-problem.html#post1031776, for example. If you look closely at the Google Street View picture, you'll see a bunch of broken/uneven pavement near the sidewalk.

There was a recall on the 3rd gen (2010) ONLY to improve the behavior which many on PC felt (w/o the fix) was worse than on the 2nd gen. It was known as SSC-A0B. I don't have a good set of threads but http://priuschat.com/forums/prius-h...announces-voluntary-recall-2010-my-prius.html and are http://priuschat.com/forums/prius-h...ius-abs-brake-recall-in-less-than-minute.html two of them.

See http://priuschat.com/forums/prius-hybrid-news/76158-prius-brake-recall-little-more-information.html for a bit more. Unfortunately, Doug Coleman works for TMS USA and likely doesn't cover Australia.

 

There are similar complaints for the FJ brakes too, especially braking over rail crossings and certain other conditions like manholes. The FJ brakes are also electric assist.

Perhaps a combination of how electric assist works, and the programming of the ABS, all conspire against you in certain conditions

With the FJ, one can induce a failure mode that disables the ABS and VSC, along with the Traction Control. What happens then, if you try to recreate the braking over rail crossings, the brakes just lock up but you stop much sooner

ABS was NEVER intended to actually shorten braking distances. ABS was designed to maintain control in most conditions. Indeed there are conditions that ABS will increase, sometimes dramatically increase, braking distance

My FJ owner manual has 2 pages with those sort of warnings, many highlighted in yellow.

 

What is happening when this occurs is your tires are losing traction and the ABS, Traction Control, and/or ESC systems, one or all, are trying to compensate. This will happen over railroad tracks, tiles that get slick when wet, cat eyes, or anything that causes your tire to lose contact and/or traction with the road (ie driving fast enough over a bump, rock or other that make the tire bump up off the road for a split second). These systems are more sensitive in some cars than others. With each successive generation of these safety systems, they are refined more and more to avoid these issues. Think of driving along a dry road and then during a curve in the road you have an ice patch. Even with these safety systems in place, you will most likely lose some control if you're going fast enough. It sounds to me your car is working properly, but get it checked out to be sure.

 

I suspect what happened here was not increased acceleration but the reduction of braking force as your tires lost traction momentarily. This will feel like acceleration because when you're in the process of slowing down and the braking action is suddenly disrupted for a split second due to loss of traction, you'll feel like you're lurching forward. My dad used to to pump his brakes all the time when stopping - it was annoying because it always felt I was getting whiplashed every time I rode with him.

 

Yes absolutely. It's amazing just how many people describe it as an actual acceleration when any kind of reality check would convince you that this is not feasible.

Certainly if the Prius did truly surge and accelerate (forward) when you were pushing firmly on the brakes then I think we could all join in with Jim Sikes in a Toyota class action free for all.