Is there something wrong with my traction control ?

http://priuschat.com/forums/gen-iii-2010-prius-main-forum/63956-floating-feeling-when-braking.html

http://priuschat.com/forums/gen-iii-2010-prius-main-forum/67528-braking-problem.html


http://priuschat.com/forums/gen-ii-...nintended-uncommanded-acceleration-issue.html

 

I had this feeling twice. It didn't feel so much like the car accelerated, just that the brakes released for a split second. I never experienced this in my Gen II.

 

I'm pretty sure this is a known behavior of the Prius and is an effect of the braking system switching from regen to disc....somehow need to find a way to anticipate and react accordingly when it occurs.

 

Normal behavior.

 

Hold on a second...I understand that it seems like everyone knows about this (well, almost everyone) and that it is a well documented and well known problem. However, a problem like this should have been fixed by now, considering this problem has been around since the Gen II models. Hopefully, nothing has happened to anybody. Unfortunately, I can think of more than one instance in which a person or animal could be seriously injured due to this problem. God forbid, but imagine you are driving into your garage, there is something in the way that acts as a bump, you lose braking force for a split second and your three year old happens to be right in front of you...the split second you lost due to the regenerative braking could be the split second that could've saved your son/daughter. I know I am being fatalistic, but I am not necessarily exaggerating. Honestly, better safe than sorry, right? Hasn't Doug Coleman said anything about this?

 

The "problem" is an illusion: it *feels* like the car is accelerating forward, but what's happening is that hard braking is being interrupted when the car loses traction, and that sudden loss of deceleration feels like acceleration. One cure is to give yourself more distance for braking.

 

If you are coming into your garage fast enough for your front tires to come off the ground you are about to go straight through the back wall anyway.

 

I don't believe for a second that the car "decided to give gas to one or both of the wheels". This doesn't make any sense at all. I assume that one or both of the front wheels lost traction and the braking system switched to friction brakes. That action is well documented, and is not a safety issue unless you overdrive the conditions. The sensation of acceleration is an illusion. The car is still slowing down, but for a brief instant the rate of deceleration drops to near zero. This feels like acceleration, but it's not.

Tom

 

I haven't had this happen to me in my Prius yet. It's only two weeks old. But I've had something that sounds similar happen in my (traded in clunker) Ford Windstar frequetly when breaking over bumps. It's a very disconcerting feeling that I learned to live with. My Windstar seemed to be very sensitive to this. My wife's Accord would break fine over the same bumps. I've always hated the feeling of ABS, just feels wierd to me.

Michael

 

Maybe the three year old likes to play in the potholes in the garage!

 

Thank you for pointing out the fact that this is not a Prius-only situation. This can happen with any car that has ABS.

 

This has happened four times on my new Prius within the first three weeks.I was not going fast and just applied the brakes. The first time I almost hit the car in front due to a surge in power. i am taking it back to the dealer but was told they may not be able to solve it unless it behaves the same way on a trial run!!!

 

:faint:I was sitting in line waiting to approach a gas pump with foot brake on, and then creeped forward where upon the brake pedal sunk to the floor and the Prius DID NOT decelerate and I almost bumped the vehicle several feet in front of me. That felt like acceleration to me ! Where is the "illusion" in this situation? I can't recall if there was a bump going from asphault to concrete. If a vehicle doesn't stop when brakes are applied, I think that there is a definate problem in the braking system :boxing: !

 

I think that some of the problem is that many of us Prius owners like to increase tire pressure. When I play with different tire pressures I notice that the frequency of the "illusion" increases as tire pressure goes higher. In fact it completely went away when I bought new tires last year. My suggestion is that if it worries you lower the TP to the suggested TP from Toyota or buy a better set of tires.

 

The ABS kicks in because the tire temporarily leaves the ground when you hit the pothole. Softer tire (lower tire pressure) allows for more grip and grippier tires just have more grip! What do you expect on 60K miles tires

Try driving off a track and hit the grass or ice-patch, you are not really accelerating, yet you feel like you are speeding up.

 

Since the theory behind the loss of brake pressure is that it is related to a loss of traction which results in the car switching from regenerative brakes to friction brakes, would it make sense to say that perhaps the reason you notice it less on new tires is because they have brand new tread and thus have better traction? Is there a correlation between the proper tire pressure and traction? It's too soon for me to tell since I've only owned my Prius for a couple of months and the tires are still in very new condition, but I would not be surprised if the loss of brake pressure becomes more frequent as the tires wear down.

And I refer to it as a theory because I'm still not 100 percent convinced that it is related to traction, although I must admit that since I've started paying more attention to it, it has only happened when I've hit a pot hole or other anomaly in or on the road. Of concern perhaps is that the said road condition does not appear to have to be severe in the slightest to cause the brakes to lose pressure.

 

You are partly right, the ABS engages because the wheel was able to lock up. possibly from bouncing from a pothole, or from the tire losing traction on a puddle or oil slick. The purpose of the ABS is to keep the wheel spinning so that it allows you to easier control the car without going into a skid. Like I said Better tires and or Lower Pressure eliminates this problem.

 

The situation you describe is not the one discussed in this thread. When you are creeping all braking is friction, so no transition from regenerative braking can occur. Your description is the first I have heard of this, so it may be a new or unique problem.

Tom