NHTSA Tracking Braking Loss on Prius Hybrids

I do understand your concern and the article is quite interesting reading.

I do hope that Toyota does investigate the issue and either come to some sort of fix for this issue that you seem to experience on a most often basis.

I don't get your justification for the following, from your article:

"(While he initially was looking for a fix for the problem, Becker now wants a full refund of the purchase price of the vehicle, something the company is unwilling to do thus far.

“It makes me question Toyota’s commitment to customer service and safety,” Becker says

Because there MAY be some sort of issue you want a Full Refund of your Purchase Price???

The correlation is certainly not clear to me. But I hope Toyota will look into this issue since many experience it and either come out with a fix or TSB to resolve it.

 

I've experienced this just one time in 12.000 miles in my Gen III. I don't recall it ever happening in my '05

It'll be interesting to see how this plays out.

 

I have felt this loss of braking as well- right in front of my house! There's a rough transition from the aspalt road into my gravel drive and one day, coming home from work, I pulled off the road and pressed on my brakes- and the second I felt the front right tire drop down off the asphalt my brake pedal bottomed out. It went from feeling like a brake pedal to feeling like a clutch pedal! I thought I was going to continue to move forward and take out my mailbox and garbage cans, but I pushed harder and it stopped. Another person might have fared worse and it has caused me to adjust my driving/braking behaviour when on roads that are anything less than smooth and pay particular attention for tracks or potholes!

Toyota really needs to look into this!

 

Interesting timing to see this. I've been thinking that I should file a complaint, though not sure of who to file it with, about this very issue. If I am in an accident someday because of this, I want to be able to say I have already raised the issue. I have experienced it numerous times and it is easy to recreate.

 

I did a quick search on anti-lock brakes and found the following quotes from an article on brakes published by the "Manitoba Used Car Dealer Association"

"Road hazards that will cause the ABS to function unexpectedly are gravel, sand, ice, snow, mud, railway tracks, potholes, manhole covers, and even road markings when it is raining.

The ABS cannot make up for road conditions or bad judgment. It is still the driver’s responsibility to drive at reasonable speeds for weather and traffic conditions. Always leave a margin of safety."

This article was not written about the Prius, but about anti-lock brakes in general. It actually is a fairly good article, so I'm including the link here:

Anti-Lock Brakes?

As I've posted elsewhere on the forums, I've never had any problems with the brakes on my G2 Prius. In fact, the few times that I've really had to stop quickly, the car stopped so quickly that it took me by surprise. If I hadn't been wearing my seat belt, I would have hit the steeing wheel.

I can't speak for the G3. But I can speak for the many rental cars that I've driven for work over the years. The cars that I've had AB problems with, when traveling over dry but uneven roads, were not Priuses. Most of the time they were Fords, and they gave me quite a scare the first couple of times. But now I know what to expect when driving those models.

 

I never feel the pulsing of the antilock brakes when this problem occurs. It simply feels like a delay between the time regen brakes cut out and friction brakes cut in. It's less than a second but CLEARLY noticeable and WILL wake you up. ABS may be involved but it does not appear to activate as I've activated ABS on ice and know what it feels like.

 

It's not just the ABS. It's because the newer model has better regenerative braking and it relies on it a lot. So when your braking heavily and one of the two tires braking slip, it seems like a really big loss before the friction brakes kick in. I've felt it too, and it is jarring. It worries me because it does seem like enough to cause a wreck, but at the same time, I want that awesome regenerative braking. /shrug

 

Thps issue definitely exists and I am sure ut is bot ABS kicking in. It has happened atleast 10 times in 18000 Mi I have driven. First time it was scary. Now I am not scared anymore, but the issue is definitely noticeable.

I agree Toyota should most certainly look in to this. I feel it should be more of a software issue.

 

It sounds as if a small, skid pan is needed to replicate this problem:

1. cardboard-on-cardboard - two cardboard sheets with one on top of the other and brake so one wheel passes over the stacked sheets. Does not require special weather.
2. ice patch - find a frozen puddle and again brake so one tire will pass over the frozen patch. Requires sub-freezing temperature.

Christmas Day promises to be dry and the work parking lot will be empty. Cardboard is in ready supply (or soon will be.) Setup a video record on a tripod and 'do the experiment.'

Bob Wilson

 

I experience this on both Prius , Gen 2 and Gen 3. It only happens on slippery pavement and I personally want that control to prevent skidding. I almost know when the brake pulsing is going to happen and I adjust my speed based on the road conditions. The feeling can be very frightening to other drivers, especially if you are so used to other car brakes that just grab as you jam on the it.

I am still not convinced if this is a real issue or not on the Prius. For now, I keep my speeds down if road conditions are not up to par. Drive Safely everyone.

 

What I have found is that when braking to a stop, if a wheel slips (ice, pothole, etc), the rate of de-acceleration decreases momentarily. That is the surge that people talk about.

What I want to know is: 1) what impact does that have on stopping? 2) does it occur in a panic situation? 3) as a practical matter, if I am braking to a stop and it occurs, does it really matter (i.e., I am braking lightly enough that it is regen braking...if I was braking hard, it would be friction braking).

 

I can make this happen every day. As I go down a hill towards a light here's one large bump that's guaranteed to cause the slip. I've never had a car do this before, not my Saab, Audi, Ford Explorer, or Subaru to name a few.

A random thought - does anyone know of any reports of this happening in the FFH? The TV ads talk about regenerative braking - at least that's what I assume when the girl says its cool because it charges the battery when she breaks. I haven't researched this (yet). If it doesn't happen on the FHH, I'd wonder why it happens with a Prius.

 

Where it always catches me is turning from a main road into a parking lot. On a 45mph road, I'm braking through the turn into the driveway to minimize the effect on traffic behind me and as the right front tire crosses the metal storm drain grate, it triggers this effect. First time, it really freaked me out and I felt like I was about to barrel into a car coming out of the parking lot. Now that I know to anticipate it, I can be better prepared, but the sudden loss of deceleration sure feels like a surge forward and it is extremely disconcerting. And to this day, it still catches me off guard sometimes when it occurs in a new place that I wasn't expecting. It has yet to cause any actual harm, other than perhaps the soiled undergarments of my passengers (I didn't ask), but I sure wish there was a fix for it. I'm a pretty mild and careful driver, always under the speed limit, braking early, etc, so to find myself feeling like I've lost control for no apparent reason is more than a little annoying.

 

I've had it happen two or three times now and it is certainly one way to get your heart beating faster! The last time it happened I was on hill using regen braking and I hit a pile of wet leaves - bang and braking just stopped. There was no ABS or anything when it happened. I pushed harder on the brakes and braking resumed.

Since then we have had some snow and the ABS comes on - alot as it should and is completely different to what happened above.

I am beginning to wonder if Toyota have bitten off a little more than they can chew with this latest Prius?

 

Do you think that the Gen 3 is any worse or different than the Gen 2? I am curious whether it is a bigger problem with the Gen 3 or if we are just getting additional Prius owners who are complaining about an issue that has existed on the Gen 2 Prius since 2004.

Personally, after understanding how the system works, I don't think it is a big deal at all. It is a design trade off that was made to maximize regenerative braking. It is one of the quirks that reminds me that all is not as it seems in the braking system. It is actually amazing that the brakes feel as "normal" as they do when you think about how the system actually works. The brake pedal resistance is just an illusion, and the Skid Control ECU is actually applying the brakes for you.

If you are driving at safe speeds for the conditions and not tailgating others, then there should be no additional hazard. JMO.

 

I have no knowledge of how the system actually works but I have a question based on having experienced this numerous times. If it is an issue of the delay between regen brakes cutting out and friction brakes cutting in, why is it not designed so regen brakes cut out AFTER friction brakes cut in? I suppose it could already be doing this but they have not figured out to have this transition occur more seamlessly. IMO, they have done a great job with the regen -> friction that occurs at 7 MPH as it can be felt but barely.

 

I have wondered about this as well. I would speculate that they do not want any regen braking to occur once the decision has been made to activate ABS. ABS can only work with the friction braking, because they have to cycle the apply & release solenoids as fast as needed to prevent wheel lockup. If regen braking is occurring on the front wheels, that would be another force tending to stop the front wheel rotation.

I don't know why the transition can't be faster, but I believe that some people perceive it to be longer than it is. It is literally a half-second or less when I experience it.

 

This braking situation with the Prius reminds me of the comments several people would make when ABS first came out. They were not familiar with the pulsing and I was personally in a car (not driving) that someone ran through a stop sign (fortunately with no accident) when they let off the brakes when they felt the ABS kick it. People had a tendency to let off the brakes when the pulsing started, as it was different then their previous experience while braking. It is very similar with the Prius, when a large bump/obstruction is encountered, there is a transition. Once you get used to it, the transition is expected and it does not seem abnormal at all to me.

For those who have not experienced the Gen II traction control, it would be wise to familiarize yourself with the way it works also. It is also different and can be disconcerting if you are expecting one behavior and learn the Prius has a different then expected behavior is snow and ice.