Prius Brake Problem - CONFIRMED BY TECH

Prius Gen II vs. other hybrids and other ABS-enabled cars

I won't hazard to guess what the engineering issue is on the Prius cars. I just know it's there.

I'm just disappointed that it's taken Toyota this long to acknowledge it even exists.

BTW, do people with Lexus or Camry hybrids notice the same issue?

 

And you may be completely accurate in your assessment. However, Honda seems to have done a better job of managing the transition from regeneration to hydraulic.

 

Re: Prius Gen II vs. other hybrids and other ABS-enabled cars

Have they? The only 'acknowledgement' that I am aware of is regarding the Gen III Prius. Is there an official acknowledgement from Toyota about Gen II Prius brake transition issues? If so, do you have a URL (or, a pdf)?

 

Did anyone else get the e-mail from Toyota (titled Toyota Motor Sales President Answers Consumers' Questions)?

Time to get your Gen II questions in for Toyota.

 

Yes! Thats the intersection! I agree, doesnt look like metal, I will confirm tomorrow on my commute. Maybe I was assuming it was metal and thinking that was part of the poor traction problem as opposed to some larger problem with the car from hitting the uneven surface.

 

Re: Prius Gen II vs. other hybrids and other ABS-enabled cars

You're right. But, I was thinking they wouldn't admit it with the Gen III either. Now they've finally admitted it.

It's a start...

 

There isn't much to manage, since the Honda's have much less regeneration. In other words, Honda may have handled the transition in exactly the same fashion as Toyota and Ford, but it will appear to be better because there is less to start with. It's like saying that starving people are better at controlling their weight, when the real reason is they have no food.

Tom

 

Re: Prius Gen II vs. other hybrids and other ABS-enabled cars

LaHood: Getting Toyota to recall took "enormous effort," calls automaker "a little safety deaf"

 

A few people have suggested this here, but I haven't seen a cogent explanation to back it up. That is, this is one of those things that sounds like it's at least plausibly intuitive -- but until it's translated into how that impacts the actual braking system, it's just supposition. (I have yet to see any statements here that suggest this is anything more than conjecture by the people stating it.)

Regardless of the size of the motor used for regenerative braking, both systems have to manage a transition from regenerative brakes to friction brakes.

So what is fundamentally different about the transition on a Civic hybrid, given its smaller motor?

And if the smaller Civic motor necessitates a system design that produces better braking performance, then perhaps Toyota ought to mimic that -- even if it means giving up some efficiency. Think of it as a performance- vs. eco-braking mode. (Personally, I prefer the option that means the brakes are actually there when I expect them to be. )

 

Re: Prius Gen II vs. other hybrids and other ABS-enabled cars

I hope Toyota gets with the program. However, given the culture of safety deafness, I am not exactly optimistic.

I am wondering if it will take a class action lawsuit to get Toyota to focus on the Gen II problems.

 

UPDATE: There may be relief for Gen II owners - Early Priuses may have braking issues - Autos- msnbc.com

File your reports with NHTSA if you have had a problem with the brake system of the Gen II Prius.

 

How would a multiple quote have been relevant (or kept the thread tidy)? Each reply I posted was on a different subject. Or, different time separation. Am I missing something?

 

I have been following this issue with perceived loss of brake effectiveness over the last day or so. I say 'perceived' because I do not have any evidence that can prove that the brake effectiveness is really lost when compared to a skidding or spinning wheel in any other car under brakes. It is amazing how quickly it has raised its head over the last three weeks, and it does not help me not being able to get onto PC on a regular basis over the same period. It has, however, given me a chance to read through all the different threads and try to gather the facts among all the hyperbole that is flowing on both sides.

I, personally, have experienced the issue a number of times in my 07, and now, after reading all the examples put forward, feel that I could reproduce the issue on request. Any communication with Toyota or any government body should, if possible, include a reproducible scenario. From my software background, if someone gives me a reproducible problem, I can then find the fix, so I would expect the same will apply at Toyota. My experience has all been at relatively low speed, and it was certainly a little frightening the first couple of times it happened, but as I did not get into any trouble or even come close to any other problems, I have learned, as have a number of other posters have, to live with it, and just try to take a little care.

I have found this thread very useful as a number of people have attempted to not just complain, but explain what is going on with the car. I think that hm800x has given a very valid explanation of what may be happening, and it got me wondering whether the same issue would occur if the car was rear wheel drive rather than front wheel drive. We have ABS trying to keep control on the front wheels, while TC is trying to disengage that same control to protect the drive train. I think that the TC is currently being given priority over ABS at the initial point of loss of traction on the one front wheel, and possibly that priority should be reversed. I say that the priority is on initial loss, but the ABS obviously takes over after just a fraction of a second (yes, it always sems to be a lot longer, but that is just the adrenaline kicking in with the apparent loss of brakes). This time when the two systems are in contention may be different for different speeds - might explain the different observations quoted above - but I would be surprised if it was.

Can I live with it? - Yes, now I know what is happening and can adjust my driving to cope with it. I know that the friction brakes are still available if I really push my foot down (and probably intuitively knew this after the first couple of experiences), so I still feel that I am in a safe car.

Do I want a fix? - Yes, because any fix will improve the situation and make it less of an issue, and it will, hopefully, lessen the chance that other members of my family will experience the issue. Although I have a fear that the reaction will be a fix that ends up damaging the drive train just because I hit a pothole - then I do not want the fix. Which then brings me back to whether I can live with it.

 

I've had both the abs and the incident.

Normal abs, momentary reduced braking then normal abs stopping

incident - feels like the brakes completely release and if you don't press harder the brakes do not come back to your pedal pressure. What they call brake feel. Cesna, imagine if your flying and someone moves your trim all the way to nose down. That is kind of what it feels like. It doesn't happen often. Its not normal. Hopefully the software that goes in my car will fix it. Then it will be no big deal.

 

Thanks to everyone for commenting on this issue. I logged on this morning and did a quick search to see if anyone else was experiencing the same brake issue over uneven pavement. I'm surprised and concerned that like me many of you are experiencing this issue. It is always a manageable situation, but attempting to brake on uneven pavement is always a bit unnerving; The traction control light blinks, and the car seems, for just a moment, like it is unable to stop. Also, if you are braking and roll over a manhole cover or pothole, the same thing occurs - a momentary slippage of the brakes, traction control light blinks, etc. The car always stops in time, but i've never experienced this in any other car that i've owned and all my cars have had abs brakes.

I guess the only option we have is to wait for Toyota to recognize (or acknowledge!) the issue. My only thing is I don't want to wait too long. Now that I know I'm not alone, I'm even more worried about toyota quality. I bought my 2009 in June 2009, maybe it is time to start looking again at another automaker to replace my prius. A Real Bummer!

 

This is the "brake cutout" issue described in any number of threads. All Prius do this, but not all Prius drivers have felt it. It occurs when loss of traction forces a transition from regenerative braking to ABS friction braking. The ABS friction braking can come in with less braking force, producing the "floaty" feel that you describe.

The problem is worse with the 2010 Gen III, but at present there is a recall for the Gen III that changes the ABS software to improve this sensation.

Tom

 

Do you feel that it impacts your total stopping distance any? In my informal testing, comparing my 2005 Odyssey with the Prius, the Odyssey FELT better but stopped longer over wet uneven surfaces where ABS kicked in. Either in a controlled slowdown over the uneven surface or in a hard stop attempt. Prius slowed faster and stopped shorter despite that momentary sensation of "float". Both cars are rated similarly in 60-0 stopping distance (with some variation between testers of course).
I'm planning to retest this when the weather gets bad enough with some instrumentation instead of just my 'feel'.

But what surprises me is that we haven't seen any kind of formalized testing or demonstration (think high speed camera and hyper accurate accelerometers, controlled environment, pro drivers) from either Toyota or NHSTA to show just what is happening. It's all just people saying what they felt.

- D