Had an at fault accident - braking anomaly - like hit sheet of ice

You guys - I dont think they skidded on oil or gas. Ive experienced this and so have others in their Prius!

Its scared the crap out of me and Ive only had the car for 3.5 weeks. A red light that I stop at near my house has a few imperfections in it, its slightly bumpy about 200' and leading up to the red light. If I stop too quick, the Prius seems to think Im on ice/gravel or whatever and the brakes seem to respond in a manner that would keep it out of a skid = not work at all. Ive had the ABS kick on before so I know its functional. I think the car thinks its doing you a favor by not locking the brakes but pushing on the brake pedal harder does not make any difference!!

The next time it happens (Ive learned to brake differently at that intersection because it almost caused me to rear end somebody twice) Im going to let off the brake and reapply. But it DOES happen and I was NOT skidding on diesel, gas or black ice.

Its unfortunate it cost the OP an at-fault crash. I could've posted this same story the first week I had my Prius but luckily the light turned green and I was able to swing over in the next lane.

 

Sorry for your experience. This is a good reminder for everyone to practice emergency stopping in controlled conditions to experience exactly how the car will respond. I also agree that you should apply maximum pedal force during the entire maneuver.

 

No yours is different, and normal. What you are feeling is documented everywhere and is more of a human error in perception than any problem in the real world as determined by physics.

When the wheels are at different speeds, such as one going over a bump, one falling into a pothole, going over gravel, going over a washboard surface, etc, the regenerative braking system cuts out. When that happens, there is an immediate more forceful application of the friction brakes. If you measure on an accelerometer you will see that you did not speed up, you did not stay the same speed. You continue to slow down, but the rate of your decelleration, decreased. Technically in the world of physics, your jerk decreased. Humans are horrible accelerometers, and when jerk changes, we think acceleration changes. (Note that acceleration can be positive or negative, i.e. acceleration or decelleration in vehicles).

There are numerous threads on here that explain it. Since you have a reproducable area, grab your phone and run the accelerometer on it next time in a graph. You will see the line go down down down as you brake, then go down less steeply. Never go up, and not stay flat.

 

Oh the car definitely did not speed up at all, I never said that. Im sure it continued to slow down just not under its own friction braking power. The friction brakes never engaged in spite of me pushing hard on the brake pedal after hitting the bumps in the road. It felt like the car was gliding. I had to swerve into the right lane to avoid rear ending the vehicle already stopped at the light. I slid right through the intersection, thankfully it had "just" turned green, with my foot still firmly placed on the brake, bracing for hitting something or somebody hitting me. It was dry out.

Im now aware of this issue as it happened more than once. Ive read others talk about it on here and the web. Now Im prepared that IF it happens, I will take my foot off the brake real quick and reapply. I think that if you hit the brake during a bump sometimes it thinks you are sliding and prevents the brakes (friction or regen) from engaging to prevent a slide/skid.

 

I once rented a car and the breaking were similar to what you explained. I did not get into an accident. I found out later the Brake Fluid was near empty.

 

OP did not mention any bump, so I'm not ready to group his incident in with the fairly common brake transition anomaly triggered by bumps. That type is fairly well understood and easily handled.

His description sounds different. We have heard hints of other, rare brake problems, but no critical mass of reports or detail has yet emerged. I don't want any such rare but insidious issues that may still be lurking in there, to get buried and ignored beneath the one better known issue.


As for your incident, how hard did you push? Did you apply your full body weight to the pedal? I don't want people to quit pushing harder because the pedal feels like it already hit the floor and any additional force seems pointless. In case of power assist failure, manual braking mode is a legal fail-safe mode. However, it requires a much greater pedal force that young drivers have never had to apply, and that may have faded out of the reflexes of older drivers.

I keep harping on the 112 pounds of pedal force because failure at the point should be prima facie evidence of a brake defect that would force a recall. Above that point, there is no longer any confusion or ambiguity with possible operator error. See my old post:near complete brake failure on my way home from Coachella | page 3 | post post-1312422

 

What 2K1 said.

 

Just to clear up this side issue and not to further derail the OP's thread:

This is generally what it feels like to humans. Use an accelerometer and you will probably see that you did not glide with no decelleration, it just didn't decellerate that fast. There is no computer or anything in the way between your foot and the brakes. If you press, the brakes will engage. Worst case scenario is loss of power brake, in which case you need to apply more force to the pedal but it will work.

This is false. It is a good guess based on what you have felt, but it just doesn't happen. The computer has absolutely no way to prevent friction braking. It is out of the loop 100%, and there are 3 sources of power (HV battery with inverter, 12v battery if inverter/battery is gone, and capacitor backup banks in the wheels good for 1-2 good applications of brakes with no power anywhere) to keep the power brake alive, and physically impossible to prevent non-powered braking.

 

Yeah, good point. Maybe Ill make a separate thread as to not hijack. Sorry OP, my fault!

 

Emergency brakes are located just to the left of the main brake pedal (as Im sure your aware) instead of hitting an SUV, standing on an E-brake will stop the rear tires from spinning no matter what the front is doing.

 

!!

You mean locking up the back end! Yeah that'll help control of the vehicle.

You might try keeping your distance instead. That way if you come across an SUV waiting patiently at a stop sign, you have plenty of time to stop. Even works in the wet; just allow a little more distance.

 

Sas0611, I searched this site and found MANY threads and many many exact cases of this braking anomaly. Might want to share that info with Toyota Corp - its well documented on the web by Pri' owners!

Heres a good site (read the comments section) for you:
Prius Brake Failure Complaints Rising as Toyota Prepares to Launch New Subcompact Hybrid - Gas 2

 

I just rear ended someone tonight. I should have been able to stop but as I told my husband 'it was like I was on a cloud'. The car just kept going and i think it was the car i hit that finally stopped me. Dry, smooth pavement. And i feel as tho i put my full body weight behind it. Probably not more than 15 mph. Fortunately not much damage but it was a scary feeling. I absolutely love my Prius but I don't want to be worrying about the brakes. I've had my 2009 for 2 yrs and never experienced this before.
Going to try and settle this without insurance but I'm going to the dealership in the morning and talk to them about it. Not hopeful but I hope Sas0611 has luck with the corporation.

 

December 2009. That particular problem was taken care of by the recall of 2010s a few months later.

Be sure to file a report with NHTSA. I posted the link back on the first page.

 

Good idea about the release form. I have tendency to expect the best of people. And I also wanted to add that I had seen something in an earlier post about tire pressure but I just bought 2 new tires a week ago and they were on the back so I really don't think tires had anything to do with it.
I'm positive there are more out there who have similar experiences. I'll report back what my dealership says

 

i don't remember reading anything like this before, let us know if you find anything on the nhtsa site.

 

I posted that and said to read the comments - its much more revealing than the article itself. The braking anomaly problem is not ultra-isolated and it is documented on PriusChat all over even with many threads of almost the same issue in 2012. Do a search.