Prius Brake Problem - CONFIRMED BY TECH

Somebody earlier claimed this to be an issue with all hybrids, including Hondas, but I don't believe this is either merely a quirk, nor have I seen any evidence that it is an issue with other hybrids.

I can tell you that I bought my wife a Civic Hybrid back in '07, and while admittedly, I don't drive that car very often, I've never experienced the problem in that vehicle, nor has she complained to me of experiencing such an issue.

So you can count me as skeptical that this is a general hybrid issue, as opposed to a Toyota issue. And of course, that Toyota claims to have reprogrammed the software to resolve the issue (at least in the 2010 model) also contradicts the notion that this is merely a hybrid quirk that ought to be expected and tolerated.

 

Can we just address the perception of time? If you're going around 20mph, your traveling approximately 30 ft/sec. If you really lost control for 3 seconds, you will have traveled 90 ft. In my experience with this sensation, it lasts a fraction of a second and there is no loss of control for anywhere near that distance. If your not braking over that long of a distance/time, you need to have more than your brakes inspected.

Like others here, I have experienced the same in my 05. It never bothers me because I never feel out of control. Maybe it's because I grew up driving with drum brakes in Ohio winters! But I will say that in my limited experience with other cars, the Prius handles quite differently on those bumpy surfaces. (We have a lot in NYC!) Personally, I don't care for it: my old passat handled much better on the exact same surfaces, as far as the braking was concerned. However, it also had all-wheel drive.

The real heart of the matter is this: if investigation finds something is faulty, or can be improved upon with the 2010 braking, AND it can also be shown to be an issue with the hundreds of thousands of Gen II out there, I imagine there will be fix issued. Toyota has too much at stake right now. I haven't driven a Gen III to say whether or not it's the same sensation that so many of us feel, but it sure sounds like it.

But as far as I'm concerned, even though it might not feel like it brakes as well as another car, I haven't seen any conclusive tests and I don't consider my Prius unsafe.

 

Agreed. It's definitely sub-second. But it's understandable that people perceive it as longer, because when you feel like you've lost your brakes and might hit something, even a short period feels like forever....

And I can say the same for the 2WD Passat I was driving before I got my Prius, as well as every other car I had before or after!

Safety isn't a binary thing. I've continued to drive my Prius for 4 years, so obviously I don't consider it so unsafe as to have gotten rid of it. (If it weren't for riding the HOV lane here on LI, though, I likely would have.)

On the other hand, a colleague of mine bought one a few years ago, and traded it in after less than 6 months because one scare was enough for him to decide it wasn't worth the worry.

I haven't had time during regular business hours to call Toyota and find out whether they're already quietly doing the software upgrade on Gen II's. But I expect that it's just a matter of time. Even if it weren't the same issue as the Gen III has, I expect that enough people who have experienced the problem with a Gen II will feel empowered by the acknowledgment of a similar issue in the Gen III to demand a fix.

From the descriptions, though, I expect it is the identical problem. My theory is that Gen III marketing opened the car up to a broader class of consumer who was less likely to tolerate the issue without complaint, and that's why it's first come to the notice of the general public, now.

 

IMHO...it seems to me that there enough folks here with a Gen II braking 'problem' that should be filing a complaint so that something might be done about it. Or, would you rather gamble and hope you don't run over a kid or slam into a tree first?

Here ya go - Office of Defects Investigation (ODI)

 

That's how anti-lock brakes work in EVERY car. You clearly have no understanding, so I'm not going to waste my time explaining.

HINT: Do some homework - learn how autos work. Your answer is found there.

-Brad

 

Brad, I don't think there's really any way to respond to this other than to say that you ought to do your homework (by at least reading the prior posts in the thread) before you waste everybody else's time with your comments.

You are the one who does not understand (and that's because you're making assumptions about what is being said, rather than taking the time to understand such).

 

I filed a report a few days back -- told them they need to broaden their investigation to include at least the Gen II's. That was easy, since it's a 24-hour web form.

Sometime soon I'll find the time to call Toyota, to find out whether they have an unpublicized software fix for the Gen II's, doled out on request, or to add mine to the many complaints I'm sure they are hearing about Gen II brakes, at this point.

 

Actually, it often is - there are federal regulations and standards that a car has to meet in order to be deemed safe. If it were only up to perception...well...you can guess how that might go!

Agreed. Here is a quote from the first google news story on the Gen III braking here that says:

"Under ordinary circumstances, the Prius braking problem would probably not be serious enough to prompt a recall, said David Champion, director of automotive testing for the publication Consumer Reports, according to The New York Times. But given the amount of negative attention surrounding Toyota, and with two committees in the House of Representatives scheduling hearings this month about the recalls, the carmaker needs to show that it is doing everything it can to alleviate fears about its vehicles, Champion said"

Also, please let us all know what the dealer says. I, for one, would be very curious. Maybe a software "hack" will be "leaked" here on PC and those who feel it's needed can fix it ourselves! :thumb:

 

I've read through the bull - I can't state it any more clearly. Uneducated "drivers" and media hysteria are the ONLY issues with the Prius and ALL Toyotas.

Again - remember Audi? Remember the hysteria? Remember all the reports of the children being killed due to this "defect"? The same forces are at play today - ignorance and greed.

-Brad

 

I said:

Safety isn't a binary thing.

Come on. You know that's not true. That's why crash-test ratings, for example, have a variable number of stars, rather than simple pass/fail ratings.

Safety is only binary when somebody applies a threshold rule of some sort to fundamentally non-binary data. (Whether the rule is applied by the feds or somebody else is really a separate issue. )

 

So let's see, your argument is:

1) That if there was ever any overhyped issue that was purely hysteria, then this issue must be such also, and

2) That all the people who complain of this issue, even if they complained years ago (like myself and a number of others) are reacting to media hype and hysteria, and

3) That all the people who complain of this issue who have decades of experience driving other vehicles, including other vehicles with ABS, are simply "uneducated."

Well, I for one am a Ph.D. engineer. My domain is EE and CS, but I went to school long enough ago that we still had to get broad engineering training before being allowed to specialize. I also have purchased and driven no less than 7 vehicles with ABS for myself and my family in the last decade, not to mention driven many rental vehicles with ABS. Furthermore, I spent almost two decades driving vehicles without ABS prior to the widespread adoption of such. And not a small amount of driving, either. I currently drive more than 25K miles per year. Haven't driven that much for my entire 26 years behind the wheel, but I easily have more than half a million miles under my belt. It's been at least two years since I first posted my experiences to a discussion at this site.

I suspect that I have sufficient experience, a sufficient understanding of engineering principles and the scientific method, and sufficient distance from the current media hype to be able to reasonably evaluate my experiences with my '06 Prius vs. normal ABS behaviors.

Pray tell, Brad, on what vast background of knowledge and experience -- actually, more importantly, using what logic -- do you base your conclusion that since there's media hype at play, this all must be nothing more than hysteria?

(For the record, I have to travel today for business...so barring some shockingly surprising revelation of substantive insight, Brad, I probably won't reply to you further at all, and in any case, not anytime soon. I've already spent far more time responding to you than the substance of your posts warrant.)

 

I have a rational brain, and I use it. Try it next time, Dr. Doom

-Brad

 

Ok, I understand your point. I agree that there are variations on the ratings as exampled by the star ratings. But there is also a fundamental threshold that needs to be met in order for the car to be driven on the road.

I know you're getting some flack on here, I don't mean to add to it. I don't disagree with you about questioning whether this is an issue for us Gen II owners: if you find out something from the dealer, please let us know. We should all be trying to help each other on here find answers to this in a constructive way.

 

This problem has been around since the 2004 model.

Wow. There are a few very naive Toyota apologists here.

All I will say is:

1) I've had this problem since 2004 on my 2004 Prius.
2) I've read other posts about this problem for many years now at Priuschat... ie. since the Gen II Prius was released.
3) The few other cars I've driven with ABS didn't have this issue, but they weren't Toyotas either. They had the ABS that actively pumped the pedal.

 

Re: This problem has been around since the 2004 model.

Welcome to PriusChat! Enjoy your stay.

I'm a little surprised by the number of people who basically come on here and say "I thought it was just my car, but it turns out I'm not alone in having x issue" because so many community members instantly dismiss their concerns.

My other cars with ABS never give the feeling of losing braking power (whether or not the "letting go" feeling constitutes a real loss of braking power is another subject). I drove a civic hybrid and never had that experience either, although that is of a different transmission and hybrid system design.

 

A rational brain would seem to use objective facts to dispute unfounded assertions. You have been doing the reverse. Perhaps you don't have a rational brain or at a minimum, aren't using it.

 

I'm sorry, but the 'abs is not plusing' -- the regenerative braking has just totally 'disengaged' in order to prevent damage to the drive train when the sensed slipping stops. At least, that is how this behavior has been explained by many 'experts' over the years on this and other forums as a 'design feature' intended to prevent damage. A cynical view might be that the electronic 'feature' was added in order to avoid having to build the drive train sufficiently beefy [and weighty] to avoid the damage without disengaging the braking.

I suspect the recent attention to this behavior is because with more and more on the road, less of the drivers are prius huggers and more just normal drivers who expect their car to behave like a normal car [none of which I am aware of disengage their braking over potholes or manhole covers].

[07 prius, 65k miles -- and driving it carefully]

 

I think no one ever analyzed this supposed brake problem on the mechanic side of the thing to realise that it can be simple hybrid car characteristic. I really think that this feeling of brake power lost can happen to any hybrid capable of regen braking and cannot happen to regular car equiped with friction brakes.

Here is my though about this.

On a regular car, when you apply brakes, you apply friction brake to all 4 wheels. On hybrid car when you apply brake you get regen braking power on the 2 front wheels only. Don't panic here, you car is still equiped with friction brakes on all 4 wheels like any other car and actually use them if you push hard on the pedal or switch fast from the acelerator to the brake pedal (panic situation detection mechanism).

It is also important to know that since regen braking power is electricaly generated by the hybrid electric motor it has to through the hybrid transmission, differential, drive shafts, wheels and finaly the road. In comparison to regular car with friction brakes, the braking power only has to go from brake disc, wheel and the road. The important thing here in this brake power path difference is the differential.

I'll explain a bit what is the differantial for those needing it. The differential is an arrangement of gears that split engine power to the 2 drive wheels. All cars actually need differential to split different power ratio between the two drive wheels to compensate for different wheel speed when you turn with your car. One characteristic on the differential is to direct all the power to the 'no traction' wheel if this situation occur. Everyone ever experienced this characteristic when trying to accelerate on a splipery road and ending with only 1 wheel spinning.

Now back to regen braking that is generated by the hybrid system. This braking power (just like acceleration power) has to go through the differential to reach the wheel and the road. Now what do you think will happen if while in regen braking one of the front wheel loose traction with the road? That's right, just like accelerating on a splippery road, all the power is sent to the 'no traction' wheel by the differential and the opposite wheel gets no braking power. This may be hard to imagine, but the no traction wheel instead of accelerating very fast like the acceleration situation, it slows very fast in the regen braking situation and consume all the braking power (in theory it can also spins backward and I'm pretty sure this happen). This phenomenom can't happen on a regular car simply because the braking power deosn't have to go through the differential.

To bring back the braking power, the car's ABS system detects wheels speed difference and now engage standard friction brakes on all 4 wheels. So in a split second, it is possible to go from 2 wheels regen braking, to a no brake power feeling, to a 4 wheels friction braking (actually 3 wheels assuming there is still 1 front wheel at 'no traction'). So this quarter second in the no brake power situation 'sandwiched' between two braking situation can feel like an acceleration surge.

I've experienced this brake power loss feeling a couple of time with my 2004 prius while going over railroad crossing or wet manhole while braking but the quarter second with no brake power was way too short to end to a collision.

Some people seem to have experienced longer period without brake power. I think this phonemenom can also be explained but is more technical and the odds that the all the pieces of the puzzle can get in place are soooo small. So let's go.

ABS system mesures each wheel speed with pulses sent by each wheel BUT the system have no indication of FWD or REV rotation. Basically pulses frenquencies are computed into wheel rotation speed but this doesn't and can't indicate the direction of this rotation speed. So now imagine that you are in regen braking, one of the front wheel loose traction with the road, the differential send all the regen brake power to this loose wheel, this wheel quickly consume all the regen braking power and you are now in this split second period of no brake. What happen now, is that the loose wheel begins to rotate backward because of the differential action and at a speed that is near to the 3 other wheels that are rotating foward. The ABS system receive pulses from each wheels that indicate that they all rotate at similar speed wihtout enough difference to triger ABS system and thus friction brake. Now this split second may last longer until sufficient rotation speed difference is computed by the ABS system to engage friction brakes on the 4 wheels and bringing back brake power to the car. I think we can agree that the odds for this scenario are quite small but I think this is technicaly possible and this is the reason that this brake power loss is so hard to reproduce.


Ok now i'm done, it's a bit ackward typing this on a netbook !!!

 

Except the loss (transition delay?) of braking ability doesn't seem to happen with the Honda Insight Hybrid....