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Toyota Prius Brake Problems



  • wwestwwest Posts: 10,706
    Hybrid vehicles, unlike ABS implementations in non-hybrid vehicles, have two modes. Mode 1 simply disables regen braking and brings frictional braking online if it is not already. This transition, when frictional braking was not already online, is the cause of the "lurch" or "surge" seat of the pants "sensor" feeling, in reality a brief "lessening" of braking HP.

    Once frictional braking comes fully online and if impending wheel lockup detection persists then ABS goes into mode 2 and you get that standard vibratory brake pedal feedback "signal".

    In the case of a short bump, pertubation, in the roadbed that causes a brief separation of a driven wheel with the roadbed it is highly likely there will be no cause for ABS to enter mode 2.
  • wwestwwest Posts: 10,706
    "...ABS is capable of PWM, Pulse Width Modulation down to 10's of milliseconds is good.."

    While electrically/electronically the solenoid voltage can be switched on and off at those rates the mechanical time constants involved only allow a "switch" rate on the order of 100's of milliseconds.

    The PWM dutycycle is controlled by the ABS ECU in real-time, and it has two "masters". First, it will not allow the front wheels to slow very much more rapidly than the rear wheels, and vice versa. Second, if it detects that ANY wheel is too rapidly approaching lockup it will instantly release brake fluid pressure on that wheel and will not re-apply pressure until the wheel rotation rate has again risen to some "target" as defined by the current roadspeed.
  • phydophydo Posts: 1
    Might as well add my two cents worth here. My 2005 Prius (bought new) acts as if I have slammed on the brakes with only a very light touch on occasion. Mostly mornings. This since the very first year I had it. Toyota of Tampa Bay says they know nothing unless they see the problem. Even just an amateur search on the web shows this is fairly common problem. I filled out the little complaint form at the DOT site of "Office of Defects " and I received back a notice saying if I wanted to file a complain this number.That after already filling out a complaint form. LOL. I notified Toyota but they have yet to give me any indication that this is something they are interested in fixing. It's OK though I have kept records and so if we get in a wreck at least my kids can sue everyone involved and maybe get a few bucks out of the criminals.
  • carnaughtcarnaught Posts: 1,577
    Do the brakes WORK; i.e, do they stop the car?
  • bwilson4webbwilson4web Posts: 80
    edited February 2010
    I'm still testing but preliminary data indicates A0B fixed the brake pause. I used the following pothole for pre-patch testing:

    The pothole, near side, was used for testing: ~4-5 inches deep and 7 feet long. I approached the pothole at ~20 mph since 19 mph is a documented threshold for braking transition. Before the patch, the regenerative indicator showed ~75% but after the pothole it dropped to ~20-15% and there was about a 50% reduction in braking force:

    After the patch, the same test scenario showed ~50% regeneration and no reduction in regeneration after the pothole. Accelerometer testing showed no reduction in braking force:

    It took a while to realize that the brake pause was not the same as our rain-slick Huntsville streets. I have one more test to run but it will take drizzle wet streets. But based upon the pothole tests run on Saturday, Feb. 13, the patch A0B works.

    Bob Wilson
  • dmaysdmays Posts: 7
    I have a 2007 and a 2010. The 2007 has always had this type of issue. Living in NJ I also notice it on snow and ice bumps..especially with the recent snow accumulation.

    The 2010 has not engaged the VSC or AB as much as the 2007...but it has happened.

    I honestly take this as normal...a Prius may start with a P but it ain't a Porsche.
  • Couldn't figure out how to edit my original post, so I just replied to it. I did find that the ABS brakes were working BUT only if I pushed the brake pedal down far enough. On snow and ice, I don't mash them - I have always applied them lightly. Anyway, I still apply lightly, but if I need the ABS to kick in, I'll go ahead and push them down til the ABS kicks in. It does help me stop. My dealer also disabled the beeping in reverse for me. They tried to use the "but how will others know when your backing up" line, but when I responded that I wasn't sure how an internal sound was going to help those outside of the car, they agreed and did it for me.
  • I have also experienced the surging (brakes disengaging) in my 2010 Prius II. Like others, it happened as I was braking and ran over some rough spots in the road. It really felt like a surge, but I can see how it was the brakes disengaging. It's happened twice now - I can totally see how someone could rear end someone.
  • wwestwwest Posts: 10,706
    "..It does help me stop..."

    Pushing down harder on the brakes will always help you stop.....EXCEPT if you push so hard or the road is so slippery that ABS activates. There is no condition known to man wherein Anti-lock braking will not extend your stopping distance.

    The idea behind ABS is to "reserve" a portion of your front wheels' roadbed traction coefficient for directional control. The bad news is that it will do that regardless of whether you need, or use, that "re-apportioned" lateral traction.

    Some day soon I expect that VSC will be used to activate ABS only if it is needed.
  • carnaughtcarnaught Posts: 1,577
    I have also experienced the surging (brakes disengaging) in my 2010 Prius II............ It really felt like a surge, but I can see how it was the brakes disengaging. It's happened twice now - I can totally see how someone could rear end someone.

    That's one of the reasons why it's not good to tailgate.
  • wwestwwest Posts: 10,706
    edited February 2010
    Trust me, you don't have to be "tail-gating" in order to rear-end another car, all it takes is a momentary release, TOTALLY UNEXPECTED momentary release, of FULL/PANIC braking.
  • I had the ABS recall appointment this morning on my 2010 and learned from the dealer's service staff something I must have missed in the 450-page manual and all the media coverage and blogs.

    The car does have brake over-ride. It only works at >30mph. Feet on both accelerator and brake pedals simultaneously will stop the car.

    I have not experienced any unanticipated acceleration on this car bought in December, but I know the complaint shows up in NHTSA complaints, but not to the degree of cars being recalled for UA. I had already practiced shifting to N and killing the engine by holding the start button for 3 seconds; yes, I know the brakes can overpower any engine surge.

    I continue to like this car a lot and have confidence in the company. The bashing from the GM crowd is pretty entertaining, in any case.
  • Thanks for clarifying some of the operating characteristics of ABS. More than ever I want to have the option of temporarily turning off the ABS on any vehicle I drive.

    I'm apalled to learn that ABS is highly undesirable when driving on snow or ice or loose sand or loose gravel when what you most want to do is get stopped ! This is particularly aggravating when I think of the $1000 I invested in Toyo ice tires, that are being hobbled by ABS just when they could be most effective. Maintaining directional control seems to be a less frequent occurence to me, although mighty nice when you can benefit from it.

    On reflection, it seems to me that ABS may be largely responsible for the recent accounts of runaway Toyotas that couldn't be stopped by standing on the brakes. That's the way ABS is supposed to work ! IE: ABS will prevent wheel lock-up, and it will continue to function until the brakes overheat. At this point ABS shuts off but the brakes are probably too hot to be effective and there is no hope for the driver stop his runaway.

    Also horribly ironic when, before the advent of ABS, one good brake application could have brought almost any car to a halt by locking up the brakes in the first place!


  • That is right! I was not tailgating when my accident happened. I was starting from a stop light and the car in front of me stopped hard in the middle of the intersection for a rescue vehicle as I was trying to do the same. However, my brakes did not work at all for a few seconds as I pushed my foot through the floor. Then, w/o adjusting anything I was doing, my brakes all a sudden started working - but, I was 3 feet from the car at that point with not enough distance to stop and therefor hit them.
  • wwestwwest Posts: 10,706
    edited February 2010
    I seem to remember reading a report some years ago that statistically non-ABS equipped vehicles were slightly more safe than ABS equipped vehicles. If I remember correctly the disparity had to do with an inordinantly high number of ABS single vehicle run off the road accidents.

    "..On reflection.."

    I myself was somewhat stunned to see that C & D test wherein the Mustang took almost 1000 feet to come to a stop at full throttle and HARD braking. Being RWD I would have thought, at first thought, that the brakes would have been able to bring the front wheels, and therefore the Mustang, to a QUICK stop.

    What I forgot was that ABS would have prevented the front wheels from braking heavily with the rear wheels still being "spun" by the engine torque.
  • wwestwwest Posts: 10,706
    "...It only works at >30mph..."

    Are you saying the BTO only works if your speed is above 30mph....???
  • Yes, by a seemingly articulate service service person at 355 Toyota in Rockville, MD, this morning. If I find this was BS, I will go to the media and NHTSA. And, yes, she said it only works above 30 mph, but I did not ask why. The brakes alone could stop the car easily at <30, and would be needed in any case because killing the engine won't elminate momentum.
  • I think we're on to something here. If you think of a steep grade instead of a runaway engine providing thrust, it's possible to visualize a condition where the grade exerts more than the reduced braking force under ABS and the vehicle will never come to a stop. Without ABS the same situation could develope but it would tqke a steeper grade to overcome the more effective non-ABS situation. Once again, a situation where ABS cuts into safe driving limits.

    On a second issue: BA or Brake Force adjustment seems to be a rather ill-conceived driver aid. Suppose a prudent driver carefully removes his/her foot from the throttle and has it resting on on the brake pedal before maximum braking is required. Since there was no panic switch from throttle to brake does the braking computer remain stuck on minimum brake force? Is it only the inattentive drivers that benefit from automatic extra brake force?
  • wwestwwest Posts: 10,706
    I have had instances, extremely slippery sloped roadbed, wherein I had to resort to the use of the e-brake to bring my '92 Jeep to a full and final stop since the ABS would now allow such.

    I think BA watches the brake fluid pressure sensor to determine the rate at which brake fluid pressure rises in order to activate BA functionality.
  • ------e-brake -------
    I'm assuming is Emergency/Parking Brake, also comes up short on the 2010 Tacomoa Automatic because it's the foot operated toggle-latching style. So, in an emergency one has to lift one's left foot to find it and then it locks on until you release it and then re-apply your foot to remove braking, then re-apply your foot again to get braking. Not at all a good design for slippery conditions when your trying your best to do threshold braking! (I test drove a standard shift and it had the very nice manual, hand operated proportional brake so I was a bit disapointed on this feature --- more so as I realize how useful it is)

    As for BA sensing the brake fluid pressure rate increase, that might still miss the mark if a prudent driver is gradually applying pressure in search of threshold braking. I'll explore this a bit more. Maybe I can build up a few good reflexes.

    I'm beginning to think all our vehicles have been designed by "bare roads" designers, (regulators too, as ABS is becoming mandatory on all new vehicles.) Surely no one with winter driving experience would have put such systems (ABS, BA etc) in place. They have no place on slippery roads.
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