Braking problem

I think what he is trying to say is that Toyota has decided to have the Prius give the perception of accelerating to tell their drivers that they are driving too fast, even though the driver is trying to slow down by applying the brake.

Makes complete sense.

 

Come on now, lets not start worshiping false idols. It's just a characteristic of the braking system and this particular car. There are no subliminal message being sent by Toyota.

 

No it doesn't. Imagine......

Deep inside Toyota corporate headquarters........

OK guys what we're going to do is if any of the Prius owners drive to fast we are going to program the car to screw around with their brakes. That ought to show em. What? Wrecks? Well, just have their lawyers contact ours.

 

I'm assuming that this behavior applies to the G2s also?

If so, then I think that I experienced this effect recently, Tom. The traffic in front of me stopped suddenly, and I hit the brakes on my 2009. Wow!!!! I could not believe the G forces as the car stopped very suddenly! I also don't recall the tires sliding. Truly an amazing stopping experience.

 

Yes, the Gen IIs also have brake assist.

Tom

 

good thing there wasn't a bump in the road at the time.

 

This sounds like what I have experienced with my other cars, ABS brakes. Depending on the road surface, I do occasionally get the brakes to chatter on and off. I guess this keeps you car under control.

 

Hi

I have a 2010 Prius IV with approx. 3000 miles this has happened to me about 5 times. It seems like you have been rear ended while you are trying to slow down. The first time is happen I got out to see if I was hit from behind. I have not noticed that it was happening on a bumpy road or area of pot holes. My wife seems to think it happens when going down hill.

Anyone else having this problem. I will not be able to reproduce it so I have not brought it to the dealer to check.

Thanks

 

There is no reason to take it to the dealer, even if you can reproduce it. As pointed out above, and in the myriad of previous threads, this is simply how the ABS brakes respond when traction is lost. There is nothing wrong with your car.

Tom

 

I disagree. If there is an aspect of the car to which you are not comfortable with, you should let Toyota know. Also, I believe that this is actually how the regenerative brakes respond while going over a bump (by giving up). No?

 

Sure, let them know your thoughts, although you are probably better off doing this through Toyota and not the dealer. Since it isn't broken, there's nothing the dealer can do. The dealer might or might not forward your comments.

As for your question about regenerative brakes, going over a bump induces a loss of traction. Loss of traction forces ABS braking. ABS only works with the friction brakes, so the braking system transitions out of regeneration.

Tom

 

I agree with RobertMBecker! This is a problem. It is scary! It feels like the car jerks forward. Once, it jerked forward twice. It has ALWAYS occurred on smooth road, no bumps-grids-groves. We are really lucky no one was in front of us. So saying that that's just the way it is and deal with it is not good enough.

 

Living in the UK where we have numerous roads with "road humps" to slow traffic down, I am able to reproduce this effect repeatedly on my way home, as our road (30mph limit) has road humps along its length. One hump is set a short distance before a road off to the right, so if a car is stationary and waiting to turn right onto it I have to brake while going over the hump (we drive on the other side of the road ). The first time I noticed the problem I was behind a bus that wanted to turn right, and I lost braking and nearly went into the back of it (fortunately only doing about 20mph), resulting in me needing to apply the brakes hard to stop in time. Now I'm aware of it I change my braking accordingly, but it happens every time I go over that hump and another one that is set just before I turn left (again causing problems when behind other vehicles that are turning). Being a fairly quiet road I checked to see whether it is an illusion and started braking over the hump from 30mph (keeping the same pressure on the brake pedal throughout). At 26mph as I came off the hump the brakes disengaged and the speed remained the same for about half a second before the car slowed again as normal. From my experience it is not just an illusion and possibly dangerous in certain situations. I tried the same thing in our Renault (which has ABS and brake assist) and there was no change in braking, and several other cars I have driven over the last 6 years (all with abs) have never had this effect, which my wife has also commented on after the first time she nearly drove into the back of someone when driving the Prius.

 

It's certainly not an illusion. I'm not aware of anyone who thinks it is.

What is an illusion is the feeling of acceleration. As you describe, braking action drops off dramatically during the transition to friction ABS braking. During this interval there is very little change in speed. Many people think the car accelerates during this interval, but of course it doesn't

Tom

 

Having started a thread on this before this one got bumped up I would say the issue needs to be addressed. There are situations where it could result in damage or injury, for example a pothole close to an intersection and a pedestrian stepping out from in front of a car already stopped to your left or right. One third to one half of a second with no brakes is simply to long, even at low speed. This is very unlike the "grabby brakes when cold" problem which I have also experienced and which is pure nuisance without any safety implications.

 

Definitely has safety implications - it may only add a couple of metres to the stopping distance but that's not acceptable (especially as that couple of meters works out to be a significant percentage of the normal stopping distance at low speeds (sub 30mph). No car should have a situation where the driver is unable to judge the stopping distance accurately, especially at low speeds/junctions when cars are closer together.

 

The problem described by some as "grabby brakes" is actually an unexpexted acceleration that one cannot smoothly stop. The car "jumps" instead of "creeps" and, in confined spaces, can easily result in an unexpected collision - definately a safety problem, not just an annoyance!

 

This is a different issue - not the one described in this thread.

Tom

 

My FJ will sometimes do that if one wheel happens to hit a slippery surface, say a manhole cover or a patch of ice. In this case, rather than ABS help, it definitely hinders

 

Slight 1-foot "skid" when doing regen-only braking and crossing
a wet crosswalk marking stripe caused about 1 second
(44 feet at 30 mph) of NO braking.
There was no ABS operation that I could detect.

Apparently, even though the ABS could not do anything
(probably because the mechanical brakes were not being used),
the software shut OFF Regen Braking and did not get it back ON for a second or so.

DANGEROUS "feature" (error) in the system (probably software) design.

Can the firmware detect that the mechanical brakes are applied or not?

If it can, and the brakes are not actually applied, then a "conventional" ABS
cannot do anything. Better to NOT remove the Regen Braking unless
the mechanical brakes are actually being applied.

If it cannot detect usage of the mechanical brakes, that would
appear to be a system design "oversight".

Does the ABS controller need to detect brake fluid prssure before
activating the ABS "pulses"?

Yes, I feel that a "fix" is needed, for safety.