Prius Brake Problem - CONFIRMED BY TECH

If you want a solution, you might want to re-consider filing a report. Toyota has much more on its plate with the GenIII Prius being investigated for brake system problems.

 

Do you have a link to an online version of the MSNBC story? So far, all I have seen are references to the GenIII Prius. The GenII Prius seems to be the poor stepchild at this point. If the problems owners are experiencing with the brkaes on the GenII Prius are not reported to NHTSA, no one will get any attention for a very long time.

 

I was pretty sure he referred to the Gen II Prius, but maybe this was a mistake on my or is part. Their article says that they are recalling 270,000 cars and implies they are only Gen III cars. However it goes on to say that

http://www.msnbc.msn.com/id/35214248/ns/business-autos/

I will edit my prior post until we have written confirmation on what the NHTSA will look into...

I will however add that Danny mentions this in his first page article:

Also suggesting that the problem is the same for any generation Prius from 2004 till late January 2010.

 

I know the exact same feeling - same situation in Northern Virginia happens every time at same spot. After going over overpass, heading down it and over transition, braking gently, when hit transition, lose all braking for a second or two - traction control flashes.

Here is what I always thought was happening: When braking, in this instance, it is a gentle braking so perhaps just using regenerative brakes. When the tires hit the transition, they lose grip causing the computer controlling the regenerative braking to flip out. I assumed at this moment it is transferring from regenerative braking to normal braking and there was some kind of lag time in the computer for some reason.

Whatever is actually going on, this is a defect, seems like a computer defect, and worse, seems like Toyota knew about it. Personally, I think the traction control on the Prius is a joke. It seems not to be about traction and simply about cutting power when it detects a skid, which really doesn't help the situation. With this defect, it seems the same system that cuts power is also cutting braking power. That is why I think the defect is in the computer controlling the motors, which disconnects power (drive or regenerative) to the tires when it senses a skid.

 

I agree!

 

Turns out we all agree.

 

I think you misread my statement with two negatives in there. I agree with what you are saying.

 

deleted

 

Ooops, you are right. Sorry. Let's agree to agree then.

 

The URL that you provided specifically mentions that the GenIII Prius is the subject of the recall:

Citation: 3rd paragraph of the article.

So far, all I have seen are articles about the brake system problems of the GenIII Prius.

I don't want to sound like a broken record, but the only wheels that are getting the grease are the ones that are squeaking (and squeaking to the NHTSA in particular).

 

This is not the ABS that is the problem, it is the Traction control. Next time it happens, look at what light comes on. The traction control prevents the electric motors and engine from doing anything momentarily if the spin between the two front wheels differs too much. It is protecting the axles from excessive torque.

This is why it feels like you loose braking power when it happens. You dont loose hydraulic braking, you loose the regenerative braking.

 

I don't know why you believe what's being described is "most probably" caused by this. The symptoms described do not match.

I can tell you the symptom is not feeling the pedal suddenly get stiff as if it has hit a stop. And the symptom does not occur when the rear tires hit something uneven.

The symptom occurs when the *front* tires hit something uneven, and the symptom is a drastic reduction in braking/deceleration, not a pedal phenomenom.

I, like many others I am sure, have driven many vehicles with ABS -- between myself, my wife and my kids old enough to drive, the last 7 or 8 cars I've bought and driven had ABS.

I've occasionally had ABS kick in on those vehicles, usually in winter conditions, occasionally on gravel or sand. The vehicle behavior and pedal feel is completely different than it is with the Prius. (The Prius pedal does not pulsate when this occurs.) What's more, the Prius is far more sensitive than any other ABS vehicle I've driven, kicking in the ABS system much more frequently.

Personally, I've learned to anticipate what features on the road will trigger the behavior, and both allow more room to brake, and release my foot from the brake pedal immediately before hitting the uneven feature, in order to avoid experiencing the problem.

Still, on the rare occasion where I miss something in the road, or have a panic stop and experience, it is pretty damned startling -- heart skips a beat type feeling as you wonder if your going to hit the car in front of you.

And for the record, the vehicle has the corresponding problem with its traction control. When you are accelerating and hit something uneven, the throttle is momentarily cut back, and the vehicle stops accelerating. When I first got the vehicle, this was almost as scary, since it would frequently occur in situations like pulling out from a gas station, where the gas station lot was uneven with the road, or a pothole had developed right at the pullout -- so you'd be pulling out into traffic, and suddenly the vehicle would stop accelerating.

Again, I've gotten used to this, and most of the time plan ahead in terms of the amount of room I require before pulling out, and in terms of recognizing problem features in the road, and manually releasing the throttle in order to avoid having the car do it for me.

I've had several vehicles with traction control, and again, I've never experienced a vehicle that behaved so aggressively, or was so sensitive. Neither this, nor the braking issue is normal behavior.

I certainly hope that a software adjustment for the GEN III Prius means that a software fix for the GEN II Prius will be rapidly made available.

Time to call Toyota....

 

Maybe you should also file a report with NHTSA? Toyota has slightly more important fish to fry at the moment.

 

I may well contact NHTSA, but in my book you go to the source of the problem first.

As for Toyota having more important fish to fry...actually, I'm not sure that they do. i.e., do they want to get in front of the issue, or be perceived as being dragged along on yet another one.

My expectation is that the Gen III braking problem is the same as the Gen II problem, so the fix is the same (albeit presumably in a different code version).

And since Toyota's current approach is to fix issues on request, for all I know, it's already available for the Gen II Prius, also, and they simply haven't announced it, because they don't want more bad publicity.

If that's the case, then calling Toyota is certainly the way to find out. And if it's not the case, then calling them is the right way to make sure they understand it's not just a Gen III issue.

 

Gov't Motors? No way they care if they ever sell another car or what quality they build into their cars... Comrade Obama has made it clear that GM workers will get paid (incl. annual raises, probably), no matter what, because GM is "too big to fail".

Ford, yeah, maybe; but GM? No way I'd buy a car or truck made by an obviously failed- but perennially "bailed out" company.

 

Hi All,

Well, human perception of time is highly variable. "A second or two" may actually be less than 1/2 a second. Or, the patch or traction-less surface may last a second or two at the speed of the vehicle. Brakes on or off, your not slowing the vehicle at all on a traction-less surface.

In college physics friction is modelled as sliding and static. The coeficient of friction when two surfaces slide against each other is pretty small in comparison to static friction between the same surfaces. This is why braking a car at the extreme has a snap-loose characteristic.

I had a near miss in my 2006. I was coming around a curving road where at the center of the curve was a red light tee intersection, that was green for me on the curve. A large SUV came around the stopped cars in lane closest to me, and I did not see it till its A pillar cleared the forward most stopped car. It did not help that the SUV was grey. He was going way to fast to stop for the light. And he did not. I went to 80 % brakes, and pulled the car into the sharpest turn possible at the speed I was at. This was at 30 degree F, after some snow the day before, and the road intersection had ice patches. I felt the brakes tug and releases left and right as I made the turn. Luckily, I missed a curbing (this was at night, and there was no lighting on the center curb) to a long drive way opposite the tee interstection, and had the long drive way to brake to a stop. The SUV was side by side with me for about 5 yards, then the SUV went behind and cleared the curbing on the curving through section of the road, going the opposite direction I was. After this was all over, I could not figure out how we missed. I gotta believe now it was the ABS that gave me steering control. If this was a 1980's Chevy Citation, the car would ove looped twice before sliding sideways into the opposite corner of the intersection.

 

Thank you donee.

My car works great... stops well, tc works as expected... yay.

If you're expecting perfectly smooth braking from a car with abs on questionable traction surface you're dreaming. Go back to the old tech and get your smooth braking as you spin the car. Everyone complains because it feels weird. No one cheers when it does its job in serious situations. If this was a terrible item, why are prius crash stats so low? Yes, folks have blamed it a few times when they hit the car ahead... they should probably blame themselves. Easier to look around for somebody else when you should quit texting instead. You guys are getting your knickers in a twist as much because of watching sensationalist news outlets like city-tv and somehow it's affecting the image you had of your own experience.

Is there a case sometimes where abs isn't the best option in a given situation? Probably. There are more and more serious times when it is by far the best response. I remember all the stories I heard when seatbelts became manditory from people who thought it was safer in some particular situation to not have a belt on. There may have been a situation or 2 where that's the case, but more often than not your safer with the belt and safer with the abs on the prius.

rant mode off

 

If your car works great, I'm happy for you.

But I don't know who you think you're talking to here. Go back and search the archive, you will find multiple threads going back years discussing the braking and traction control issues with the Prius. I, myself, first posted on this more than two years ago. I certainly don't have my knickers in a twist because of recent reports. I merely view recent reports as an opportunity to actually get the issue addressed.

As I've said multiple times before, including recently in this thread, the last 7 or 8 cars I've bought for myself or my family have had ABS. (And that's not attempting to count all the rental vehicles with ABS I've driven over the years.) I like ABS. I drove cars without ABS for close to 20 years. I understand how they respond, and how to brake safely with them. And having spent most of my life in snow climates, I'm very familiar with how vehicles with ABS normally respond, and how to brake safely with them.

(Hell, I have even learned how to drive the Prius as safely as possible -- having had one for 4 years now, and being able to usually avoid the problem by recognizing the minor road imperfections that will trigger it, planning for them by allowing longer braking distances, and easing of the brake pedal myself when reaching them, to avoid the car doing it for me.)

The Prius behavior is not a normal ABS behavior. It demonstrates none of the normal ABS symptoms. There is no pedal pulsation. Somebody noted that it's actually the TC light turning on. As i think about it, that's probably true. (i.e., the light is an icon, rather than the letters ABS. The same light comes on when the corresponding traction control symptom occurs during acceleration.)

The conventional wisdom in this thread, and explained in more detail int he older threads, is that this is "traction control" kicking in to disengage the drivetrain and protect the drivetrain from wheels spinning at different speeds.

It is quite plausible to me that this is what's actually happening, and that, as some suggest the car is shifting from regenerative brakes (disengaged by the "traction control") to friction brakes. The trouble is, if that's what's happening, there is a very noticeable delay between the disengagement of the regenerative brakes and the engagement of the friction brakes.

The effect is a moment of sharply reduced, or absent, braking. The feeling is profound -- if there's something in front of you that you need to stop for, your heart will skip a beat, and you'll worry that you're going to hit it. (And yes, you can get a similar *emotional* feeling when ABS kicks in on normal vehicles. It just will be under different circumstances, and the physical feeling, e.g., from the brake pedal, will be very different.)

With some 25 years, and probably half a million miles of driving experience, across many different vehicles, I've never encountered one that behaves like the Prius, or which is nearly as sensitive to minor road imperfections as it is.

And it's clearly not just me, based on the fact that there have always been others beside me starting or responding to threads regarding the issue, reporting the same experience.

So if your Prius miraculaously doesn't exhibit the problem, more power to you. But it's far more likely that you have simply been lucky in that regard...or that *you* lack the experience to distinguish between how the Prius behaves and how normal ABS behaves, than it is that I (or others reporting the same problem) simply don't recognize what is normal ABS behavior.

 

JS - You have said it better then I could. I am in the same situation with my 2008 Prius. My one occasion to experience this problem was comming down a icy gravel road at approx 20KPH. My slight depression of my break slowed me down slightly, when I pressed harder and held there was more than a one second (Felt more like 3 or 4 seconds) where it acted as if I had removed my foot from the break entirely. Finally the normal pulsing and slowing down associated with all normal ABS systems went into effect. Both my wife and myself knew this was not normal behavier. I had intended to report this to Toyota when it happened last December, but when it never happened again I chalked it up to a glitch that will never happen again. I think I was wrong!!!!