Braking problem

I brought my Prius IV last week. Its manufacturing date is October 2010. I have experienced your incident with frequency. I have called the dealer. I am taking the car back tomorrow for their inspection.

 

Looking forward to hearing what your dealer finds and suggests: You should mention there are several posts on the Prius Chat about this "Experience", although they probably take that with a grain of salt.

See what happens and let us know.

Good Luck

 

The problen has been experienced by many, and appears
to be a "feature" of the Prius design (working as designed).

But, most who experience it (myself included) feel it is
an "unsafe" feature that should be "improved" (fixed).

I suspect that the vehicle firmware could be changed
to almost eliminate the "problem".
This update would have to be produced by Toyota Engineering,
and currently it is unlikely that a dealer can do anything to "fix" it.

 

Not only can the firmware detect that the mechanical brakes are applied, it's the firmware that actually applies the mechanical brakes. Short of an ECU failure or loss of 12V power and backup power, only the computer ever actually applies the brakes, whether mechanical or regenerative or both. In normal operation the brake pedal is nothing more than an input to the computer system. All of the braking is by wire.

Tom

 

Just curious, are you saying that in a full second you applied no more braking pressure with the pedal, which then might have activated ABS or activated Brake Assist? I would think it would be difficult to withhold the impulse to add braking pressure if you were not slowing yet you wanted to. Both those systems require driver input--either enough braking in combination with a low friction surface to cause a continuing disruption of wheel rotation to trigger ABS (a 1 foot stripe is not likely to be enough "skid" to trigger ABS and the subsequent release/application of pressure on the non-rotating wheels to feel pulsation), and Brake Assist needs to sense a panic stop situation indicated by rapid brake pedal application and/or rapid accelerator release. A slippery "spot" would cause a sensation of gliding in most any car, ABS or not, because you're losing either one or two wheels' braking. The benefit of ABS is in letting you maintain steering control when wheels are locked, which you can't do without ABS unless someone is very practiced in threshold braking. Stopping distances are not necessarily shorter.

Is it possible that the car sensed a locked wheel, and made the switch to friction braking, but then you recovered to a stable friction road surface so ABS was not needed--however you had applied rapid brake pressure during that slip so Brake Assist kicked in? Your deceleration rate would be enhanced by the additional action of Brake Assist and might give the sensation of braking "finally" being applied but in fact it was the additive braking of Brake Assist just supplementing the prior level of braking, albeit as the tires crossed a slippery stripe, each axle in turn?

'Not doubting your sensation, but I'm just curious why some sense these problems but I do not, and this is my second hybrid (Lexus). If I want to stop, I use the brake and it stops, but if I need more braking, I press harder--and the braking sensations are not unusual. The idea of "regen-only braking" just does not enter into the equation for me. Just curious about your or other's experience or practices relative to the idea of Brake Assist kicking in.

 

I picked up my '10 Prius III about a week ago and had this happen within the first day or two. When it happened I thought I must have just been imagining it- I feel vindicated after finding this thread

Basically I was entering an underground parking ramp (so going downhill) and passed over a metal drainage grate only a few inches wide, but as soon as I hit it I thought I was on ice or hydroplaning for about 1/2 second. I barely managed to stop just before hitting the car in front of me and (needless to say) had the bejesus scared out of me!

 

This is not a characteristic of a normally functioning well designed ABS system. I have owned 4 cars with ABS, including a Gen2 Prius, and have put quite a few miles on several others that were supplied by the company. I have used them on all sorts of roads and in all kinds of weather conditions. I have never encountered a problem such as this with any of them except the Gen3 Prius.

This is not the little hesitation we feel during the switch from regen to friction brakes, I know what that feels like and by comparison it is nothing. This problem is a complete loss of brakes for what feels like a full second. The vehicle will travel quite a bit further in one second with no brakes applied than it would have with brakes applied.

I have no idea why this occurs, rather it is software, hardware, or a combination of the two. I have never seen a schematic of the braking system and I don't think anyone else on this forum has. I also have no idea why it only happens to some cars and not to others, and neither does anyone else.

What I do know is that attempts to indicate it is somehow the driver's fault or that it is really normal and all ABS systems do it are just plain wrong.

It has only happened to me three times in 10K miles. The first time put my "heart in my throat" it was an "oh my God I have no brakes" feeling. The next two times I knew what it was and that helps a little. I would advise anyone who drives this car to give yourself a little extra room while braking.

 

Thanks for this new bit of information. When a new person comes on and posts about loss of braking, I immediately assume they have experienced the normal ABS dropout. In your case you know better, so I believe this is a new problem related to the 2010.

Toyota, are you listening to this?

Tom

 

I must say, I too have experienced this loss of breaking power when going over rough spots in the road. I can see someday needing to do quick breaking to prevent a collison, going over a pot hole just after slamming on the breaks, and dire consequences happening. This is indeed a safety risk.. hello! Loss of breaks?!!

Maybe instead of redesigning their floor matts to prevent them from hitting the accelerater in only very very rare occassions when the driver fails to positon them right, they should instead concentrate on this design flaw, which really is an issue the driver can't prevent!

 

There is a schematic posted, but I'm sorry I can't seem to search and find the one I want (Gen 3). Maybe someone else remembers it. It had colors to indicate different scenarios and pressure flows.

 

I woudn't call it a design flaw.. happens to me on the route to work every day.
When braking on a rough/even surface the regenerative braking turns off and friction brakes are applied instead. You may also get the ABS light come on..
Of course, the regen brakes and friction brakes do not make in the amount of stopping power. I think the Gen 3 has a more subtle switch over point...

I never drive close enough to the car in front to make any difference to my braking force.

 

This is starting to sound like something specific to the 2010 models or people are greatly exaggerating, I'll assume the former. The earlier model Prius can exhibit a reduction in braking force when going over very bumpy surfaces but nothing that would cause me to worry about running into people (unless I was tailgating AND going very fast to a stop) nor running into an intersection.

It'll be interesting to see how this pans out and if Toyota issues a TSB for a module reflash.

 

I was applying a light, steady (constant) pressure as I slowed from 45 mph to turn right. The 1-sec loss made the turn happen at an unexpected and more-than comfortable speed. No, jamming the brakes on is rarely a safe option, since it would often result in another vehicle trying to enter the "trunk" area.

I have had other ABS vehicles do similar "skid-detection" on wet crosswalk stripes, but the braking is just "modulated" (pulsed) and not "lost". Recovery to non-ABS mode was also much quicker.

 

i have driven both and still have not really felt what people describe.

now, i have felt the "slip" or feeling of acceleration etc. roundabouts that have that white raised crosswalk marker, some have manhole covers, if i hit it just right i can feel it. in fact, i tried hitting one at a higher speed just to see what would happen, but to be honest with ya, i chickened out cause i did not want the alignment damage in case i hit a curb.

but its not as bad as some here make it to be or at least

1) its no worse than what i have experienced with my 2004 or 2006

2) i have not been lucky enough to be in the situation to experience it yet.

but a "complete" loss of brakes for a full second to me would mean a spate of accidents by now, huge amounts of news coverage, etc.

do we have any of that?? has anyone gotten into or heard of anyone who got into an accident because their brakes did not work as expected? The Pri has been on the road for 6 months now, over 100,000 of them. percentages say that more than a handful would have had an accident by now and if the driver thought it was brake failure, we would have heard about it by now.

 

It is for real and it can be recreated if you have a rough road surface (we have plenty in MI). I may look around my dealership when it's time for the next oil change to find an area I can take the tech for test drive to see what he thinks. I'd like to see someone find a way to scientifically document what is happening and what the impact is on stopping distance. It is a very scary and eery feeling and sensation. I'd describe it as floating or sliding on pure ice when it happens. I love the car and won't voluntarily tell my GM loving family about this "little" problem, but it is for real. It MAY be that the loss of stopping distance is very little, IOW, it's not as bad as it feels, but it really needs to be quantified.

 

i wonder if its more of a comment on the tires used and their traction rating?

 

It's not the tires they are rated A for traction on wet pavement, and it's not our imagination, it's real. Not all cars have the problem, I'm happy for you that yours does not. It doesn't happen very often with most cars, three times in 10K miles for me.

It normally happens at low speed and if you are not following to close, which most of us do not, you probably won't be in any danger. Also once it happens to you you will remember it and compensate with longer following distances. I think that helps explain why there haven't been a "spate of accidents". It is also possible that there have been accidents that we on this forum know nothing about, low speed non-injury accidents don't generate a lot of interest or publicity.

 

r u doing the chat today?? might be a good question to bring up to see if they are working the issue

 

I am going to listen in but I hadn't considered bringing up any problems because I didn't think it was the type of forum where they would be well received. I think they are just going to take softball questions and tell us how great they think they are doing, hope I'm wrong.

To tell you the truth Dave, my car has two fairly serious issues the brakes which we are discussing in this topic, and the interior rattles. If I could have Harry Potter wave his wand and fix one of the two I would chose to have the rattles fixed. I think the braking problem may be addressed by Toyota, the rattles never will. They may fix them for 2011 but my car will always rattle, I have found some of them but I don't think I will ever find them all.

Neither of those things is enough to make me regret buying the car but I do kind of wish I would have waited until the 2011 model comes out.

 

It is easily re-recreated. It's happened to me several times. I can make it happen anywhere there is a 4-6" deep pot hole that I can get one of the front wheels into while braking.

In my opinion, the momentary loss of braking power is not what will cause the problem -- because as most people have said already, rarely should you be that close to the car in front of you.

The problem is, the first few times it happens, it scares the sh*t out of you, and most people will react by literally slamming on the brakes. I was with my wife (she was driving) the first time it happened to her, and she slammed on the brakes hard in traffic, and we're very lucky we weren't rear-ended.

The car doesn't actually accelerate -- but it feels 100% as if it does, because your brain is very specifically trained to feel significant deceleration when you apply the brake -- but for a moment, no deceleration happens, which feels like acceleration, and it is as I've said quite disconcerting.

Not sure how it can be fixed, but it should be.