Prius Brake Problem - CONFIRMED BY TECH

I'm glad you have a case that is both recognized by Toyota service (you didn't get brushed off) and reproducible. This is always the first step to a real fix.

 

I'm afraid that I do not understand the recent "problem" of the brakes. I can recreate the same problem too....on ice. You drive over something that makes the tire lose its grip on the road, and if you're currently braking, the wheel is going to decelerate at a different rate than the others. Seems like the system is working exactly as designed.

Before my Prius, I had a 2000 Corolla that had ABS (a rare option at the time for the model). It would do the same thing as the Prius.

I just don't understand what people are looking for. They want a car that'll stop in a heartbeat, even if you're on rough pavement or ice?

 

I have often seen the apparent loss of braking power when going over a washboard surface. It is the ABS dropping braking based on perceived skidding. I can get a momentary loss just braking hard over a wet painted section of road (such as crosswalks).

It feels like acceleration because you suddenly stop feeling the deceleration expected from braking. It is only for a fraction of a second.

When ABS first was introduced to passenger cars (early '70s on Mercedes Benz, for example), it was noted that although steering control inmproved from lack of skidding, braking distances increased, sometimes noticeably in the case of gravel or washboard surfaces. however, the trade-off of steering control vs. braking distance was made in favor of steering for overall safety reasons.

Remember you don't actually "brake" (using friction pads) unless you stomp the pedal or are going under about 8 mph. You are regenerating to slow the car. Recovery can be slightly slower than the 1/10 second ABS cycle time in such a case.

ABS is not a cure-all for poor driver brake control in loose traction circumstances. Like airbags and VSC, it gives naive or careless drivers a false sense of security and then they overdrive their car or recovery skills. Best advice for best traction in an ABS-equipped car is the same as it was before ABS: slow down!

 

Oh I know exactly what people are experiencing. Run over a bump while braking and the ABS comes on for a second and the light flashes. I've done it many times

 

What is being described is most probably activation of the electronic brake force distribution (ebd) system which usually occurs on ice, metal manhole covers or bumpy roards.
In situations where the abs system detects that the rear wheels are (or about to) lock up before the fronts then a valve (can be mechanical or electronic- it varies) will engage effectively blocking off a majority of the brake force to the rear wheels. The reason for this is that if the rear wheels lock even for an instant the car can lose directional stability too quickly for the abs and scs systems ability to correct causing loss of control.
The sensation of no brakes is often the fact that rear brakes are generally fairly spongy as they only do a fraction of the total braking but the EBD valve is a solid metal object. A drivers brain is more tuned to pedal pressure so this change feels like you've hit the metal stops in the pedal box when in fact it's fine.
There's two options here as a driver you can do if this happens-
1) press really really hard - push through your own calibrated brake pedal pressure and just press hard. The front brakes are still working with abs assistance and total braking force is only marginally reduced with ebd active
2) come off the brakes fully to allow the ebd to reset. Then get back on the brakes again. It's almost like cadence braking but don't go into the automated pumping action as this will mean the and system will not be working together.

I've driven many ebd equipped cars from city run arounds to supercars and they have all been the same when it's gone off - I really don't think it's a fault as such - the brake system is making a choice and picking the lesser if two evils (slightly longer stopping distance v's complete loss of control).

Abs (nd the other systems are great driver aids and do help but they are not a substitute for a driver. You still need to learn to work with them and know their weaknesses.

 

Yep

 

And here I thought they'd tried a new, patent-free way of regenerative braking and screwed up the changeover from that to the brake pads. Although this bump-stuff might be the thing they didn't test for and it interferes with the pads coming into play soon enough...

 

Your second post... clearly here to just grow fear.

Is there something that could be improved. Of course. In fact, that's why vehicles routinely get new models.

But with so many years having passed already without this causing accidents, there's nothing to actually be scared of.
.

 

I have a 2007, and have noticed several times when braking at low speed (on a dry road) and hit a pothole at the same time that you have the feeling that total braking power is lost for a fraction of a second (feels longer when it happens!). I have never experienced this on any other car.
I thought ABS was supposed to be sensing wheel rotation on each individual wheel, and if one wheel is sensed as rotating slower then it must be slipping and the ABS should be applied to that wheel. But if only one wheel hits a pothole I really don't think that the ABS should actuate on all 4 wheels ?? - or maybe Prius is different ??
The other thing I have noticed about the Prius ABS is that if I stomp on the brakes with an icy road I don't hear anything from the ABS, or feel the pulsing from the brake pedal. Other cars I have make quite a racket from the ABS when doing this. (We have a lot of ice and snow here in the Winter and I purposely wanted to test the Prius with hard braking on a slippy road, from about 15mph to a complete stop.)

 

reasoning of just 2 posts... T... R... Oooooo

qoute `he screamed when it happened`
was it a real prius MAN tech or a girly girl prius tech

ok serieus now.

come on screamed... is that not a bit overreacting

i experience this often.
at the first time i only noticed something and the VCS light came on.
i did nog even notice it after it was already over.

do you put more PSI into your prius wheels then factory stated

 

Wow, the trolls are out in force today.

 

Just kind of wondering what changed? Judging from your join date and model year, and your opening statement that you've known about this for a while and learned to live with it, I'm assuming you have had a 2008 for almost 2 years?

So what has changed this from a problem you evidently accepted and learned to live with, to a problem that you feel you must have rectified?

I'm not accusing you of anything, I'm just curious. Do you feel you're more concerned about this problem now in light of recent events? Could your opinion be tainted by recent events?

What pushed this problem from being something you lived with daily, into being something you feel must be rectified or you can't drive your vehicle?

 

I tried with my 05 Prius and a new 10 Prius on a variety of surfaces from smooth asphalt to speed bumps to potholes to drainage gratings to packed gravel to potholed gravel. I tried at different speeds from 10 mph to 30-ish mph but I can't feel the sensation.

If it can be replicated for someone else then it appears valid but I can't do it. Vehicle-specific or maybe locale-specific? idk.

 

grinthock, can you provide links to those canadian citations for driving an unsafe vehicle? Why don't they just ticket every prius on the roads (pre '10 which is not currently recalled). Also, why don't they ticket every other car that has ever been recalled but not fixed? Just seems there should be more to the story on these 2 citations...

 

Well still something has changed. First of all The Prius hasn't been recalled for brakes (as of today) and you also state now that you were told by the dealer originally that the sensation you experience was by design. So The Prius doesn't fit the definition of "unsafe vehicle". So there shouldn't be any danger of you getting charged with operating an unsafe motor vehicle.

"Yes, I was driving the car and simply living with it -- however I want it fixed now. Why? Because I decided to. No other reason"

Well given those parameters what made you suddenly decide you want it fixed now? Especially if you had the forehand knowledge that the dealer told you what you were experiencing was by design?

As an owner I think you have the right to change your mind, and decide a problem you used to find an acceptable part of owning and operating a Prius is no longer acceptable to you, but if you used to define it as "Normal" why do you expect Toyota to now define it as "Abnormal"?