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Toyota Prius Brake Problems



  • wwestwwest Posts: 10,706
    In some sense what you are describing is SOP, Standard Operating Procedure.

    With these hybrids when you apply the brakes the system is biased toward the use of regen braking, more HEAVILY biased the lower the hybrid battery charge level happens to be.

    So, you're braking moderately, using regen braking only, in order to come to a reasonably gentle stop. Then for whatever reason (pothole, railway rail, plastic crosswalk stripping, wet/oil spot, etc) ABS detects impending wheel lockup and instantly DISABLES regen braking in favor of frictional braking only.

    Note: In many cases you may never know ABS has "activated".

    Now, for a brief moment you might feel a "surge" forward due to the transition period between the time of disabling the regen braking and the frictional brake pads coming into contact with the brake rotors hard enough to reach the same level of braking you had just previously.

    Even worse if the street is oil and rain slicked ABS will kick and you you might well feel that as brakes grabbing. It is not at all unusual for ABS activation to result in elongating your braking distance in a fairly slippery surface by an extraordinary measure.
  • So, if I am understanding you correctly, you are saying that if you want to be able to stop reliably on uneven or somewhat slippery surfaces, you better drive something other than a Prius.

    Since I do not drive a Prius, I will from now on turn on my hazards when it is raining and there is a Prius behind me.
  • I have a 2006 Prius. I noticed the issue of the car surging forward momentarily when a pothole or a bump is hit (and the VSA light comes on). Like many others, I thought this was normal and just ignored it. But apparently now Toyota has recognized this as a problem, but only for the 2010 model. I went ahead and filed a complaint on NHTSA's website. I urge others to do the same, so we can get our non-2010 models fixed as well.

    Another problem I noticed is that when the road is wet, and if I was at a complete stop and tried to accelerate too fast, the car will actually kind of "slip"--it doesn't accelerate as intended but actually stalls momentarily. The way to overcome this problem is to step on the gas pedal very lightly. So with slow acceleration, everything is fine, but if you tried to rush it, it won't work. This is a severe disadvantage if you are sitting at a busy intersection trying to make a turn, because you want to go fast to avoid be hit, but like I said, trying to go faster will actually backfire.

    Has anyone else noticed this?
  • dturrdturr Posts: 70
    The main Toyota brake pedal problem is mechanical and that I can understand.

    However it is a whole new ballgame when computers start playing up.
    I just think of this thing in front of me and the problems I have, with a need to power cycle the thing every month or so. You cannot do that travelling at 70mph.

    Better the old days when brakes were a mechanical function you always seemed to have warning when things were not right.
  • I have had the same problem in my 2008 Prius. I just figured it was how the Prius worked, I didn't realize it was a problem. But I will definitely be filing a complaint now.
  • wwestwwest Posts: 10,706
    "..Has anyone noticed this?.."

    SOP, again.

    That's called TC, Traction Control. If you try to use too much engine torque for roadbed conditions the drive, driven, wheels will tend to slip. When that happens TC will activate and instantly reduce the drive power from the HSD system. Most of the time it will also apply braking to the slipping wheels.

    With a FWD or F/awd vehicle wheelslip/spin of the drive/driven wheels is of such seriously hazardous nature, HIGH potential for subsequent loss of directional control, that the TC reaction to the must be INSTANT, full and complete.

    If you happen to also be turning as you accelerate the TC (more likely VSC)functionality will likely be even more firm and sudden.

    Keep in mind that for its weight the Prius has an unusual level of get up and go from a full stop. Low speed torque derived from those synchronous AC motors.
  • wwestwwest Posts: 10,706
    " better drive something other than a Prius.."

    No, not saying that at all.

    What I am saying is that if you drive any of the current crop of hybrids that use regen braking you should be prepared for that seat of the pants "feel" of a momentary, millisecond, forward surge. In most cases that momentary "lurch" in brake application will have no detrimental effect.
  • I'm in exactly the same boat....supposed to pick up mine Friday....if you get any tips, please let me know....I'm in about you?
  • Nice explanation to the Prius braking characteristics.

    We have a 2010 Tacoma 2.7L Auto and after 16,000km (10,000miles) I am bothered by its braking performance and wonder if there are some common software/hardware related deficiencies in Toyota's products, I have two questions.

    1. This is our first ABS vehicle and it does seem to be harder to stop with ABS than our old Civic with non-ABS brakes on snowy or icey surfaces. Are there any quantitative results for ABS vs non-ABS performance?

    2. The Tacoma also exhibits unexpected brake-force requirements. Usually requiring more force than I think is warranted but occasionally responding to my idea of normal braking pressure. Is this appearing on the Prius as well as other models in Toyota's line-up?

  • wwestwwest Posts: 10,706
    1.) There are most definitely times, situations, wherein ABS is a detriment. ABS will ALWAYS extend your stopping distance in panic, severe, braking situation, in favor of allowing the driver to maintain directional. Sometimes that simply is not the optimal thing to do. I have contended for quite some time now that unless the stability control, VSC for Toyota, indicates directional control or directional correction is needed then ABS should be held inactive.

    On a highly slippery surface it will sometimes help to apply the e-brake slightly/judiciously along with normal braking. I have had times when it seemed my Jeep would never come to a final, full, stop due to continuous ABS activity. The e-brake would always help.

    2.) "..unexpected brake-force.."

    That may be due to BA, Brake Assist, if you happen to have that feature. With BA the braking system "watches" the rate at which you depress the brake pedal in order to determine if "this" is a panic or severe braking event. If it determines so then it will actually use the ABS pumpmotor brake fluid pressure to assist your braking effort. In that case it might even extend the HARD braking period should you relax brake pedal pressure somewhat.

    As a result "normal" braking will often require more brake pedal force vs if the system detects panic braking and provides the extra assist.
  • I mentioned earlier about my 2008 brakes not working properly when you hit a rough surface but I did not mention the other problem that you have. I have also had a problem with acceleration if you are on just a small amount of cinders (spread in the winter) or if it is a little slick. You step on the gas to pull out and the car stumbles and hesitates until it takes off again. It is very unsettling if you are pulling out into traffic and the nose enters the intersection and the car stumbles and seems to stall.
  • I drive a 2008 Toyota Prius and I am intrigued by the news about the 2010 3rd Generation brakes issue, since I have precisely the same problem.

    When I drive over bumpy surfaces, a large pothole, or an area with a dip in the road, the car stutters and lurches and the VSA light flashes. Sometimes the car's reaction lasts for several seconds after hitting the pothole. It seems to exacerbate the problem if I am turning or braking. I should point out that I experience this lurching and stalling sometimes when I am simply driving along at 35 MPH and hit a pothole. So it doesn't really seem to have anything to do with the brakes.

    Like many here, I kind of ignored the problem and assumed it to be a normal part of the vehicle stability function. There have been some situations where it came close to making the situation much worse.

    I also notice the problem accelerating, when the car slips and stutters and the VSA light flashes. This is usually when I am trying to pull out quickly from a driveway or make a quick turn. This is very frustrating (and sometimes scary) on busy roads with oncoming traffic.
  • Now that I think about it, you are right: I don't need to have had pressed on my brakes for the car to lurch forward and to have the VSA light come on. What is interesting is that I know for sure that my model does not have the VSA option. So I have a hard time believing that is the intended function of the VSA when it is not even equiped for my vehicle.

    For the other problem, yes it is very frustrating and dangerous in my opinion. I have had several close calls with other cars almost hitting me, when I thought I'd be able to accelerate in time but instead got stuck in traffic. If this issue is pervasive for all hybrid cars, then I am not going to buy a hybrid again.

    I do encourage everyone else to go ahead and file a complaint via NHTSA. So far it seems like Toyota is only considering recalling the 2010 model.
  • I concur - call the NHTSA and file your complaint. I have had similar occurances as you. However, my accident happened in a situation that was simply my attempt to stop in a traffic jam on a busy city street. Slow speed, pushed the brake with aggression as the car in front of me did. I would normally have stopped with about 4 feet to spare - however, the brakes did not engage until I was four feet away. Some skidding and smash into the car! In no way was the accident due to a lack of my attentiveness as a driver. Now I pay inflated insurance rates and paid my deductible for repair costs. The sad thing is that my insurance company had to pay a significant chunk of the repair costs because Toyota did not pay enough attention to detail (or ignored it). And everyone knows what happens when insurance companies have increasing claims. Everyone has higher fees - this is especially less desirable in this "buckle down" economy.
  • Thanks [wwest]

    re: ABS characteristics: Intuitively, it always seemed to me that, if one could just hold brakes close to the loss of tractrion point, then stopping would be faster than ABS pulsing which has a percentage of no-brake force at all. Thanks for the confirmation.

    re: Unexpected brake-force. Yes, our 2010 Tacoma does have BA (brake assist). I will explore the conditions you suggest will cause the variability.
  • The only thing that is good in the Prius is the gas mileage. We are averaging 47 mpg, less than about 20.00 for a fill-up. Other than that the Prius is very small, even the cabin. It is difficult to see through the back window since half of it is small. Good thing for the back up camera. My engine quit after hitting a "chuck hole" and it was difficult to start. Reported it to Toyota Service and they said "should not have happened, but no notice from Toyota for any problems". The Prius is fine for a small person but not comfortable for the Plus size person. I would not own another Prius.
  • You state: " It is not at all unusual for ABS activation to result in elongating your braking distance in a fairly slippery surface by an extraordinary measure."

    The whole purpose of ABS is to shorten your stopping distance, not lengthen it. It is a very effective system on most cars. Toyota apparently does not have the interaction of the friction brakes and regen braking worked out yet. So in the meantime, I will be turning on my hazards when I see a Prius behind me since my car has ABS that does what it is supposed to do (shorten stopping distance) and will thereby avoid getting rear ended by the half baked Toyota if there is a need for some hard braking.

    I probably should also turn on my hazards when any Toyota is behind me to avoid getting rear ended because of some unexpected acceleration event. The roads just aren't safe anymore.....
  • wwestwwest Posts: 10,706
    "..The whole purpose of ABS.."

    Is to optimize braking ability along with directional control simultaneously. Read any current owner manual to verify this. Absent ABS during hard/heavy/panic braking there is a clear and certain danger of loss of directional control due to the front tires locking and skidding. ABS activation results in allowing the brakes to exert the maximum level of braking while still allowing the driver to maintain directional control.

    Once someone develops an inexpensive (cost-effective) "linear" brake application servo system to replace the current "bang-bang" system things might improve significantly.

    Until then it would clearly be wiser to disable ABS until VSC detects the need.
  • wwestwwest Posts: 10,706
    Go back and read post #132
  • wwestwwest Posts: 10,706
    You too...go back and read post #132

    "..It seem to exacerbate the problem if I'm turning..."

    Yes, absolutely.

    If the Traction Control system detects front wheelspin/slip and you are turning then it is QUITE CLEAR that you are applying more engine (HSD) torque to the front wheels than is safe for current roadbed circumstances. This is a FWD vehicle so loss of traction, even momentarily so, on the driven and stearing wheels must be quickly addressed, moreso if the VSC system gets into the act. So in a turn wheelspin/slip will probably result in the activation of both functions, TC and VSC.

    Your Prius has an unusual amount of low speed acceleration torque for its weight along with tires that are primarily designed for low rolling resistance, not TRACTION.
  • wwestwwest Posts: 10,706
    Toyota might want to look into the methodolgy of BMW's technique wherein the brake calipers are "pre-charged" with pressure if the rain-sensing windshield wiper system senses rain.

    BMW apparently applies just enough brake fluid pressure to the calipers to bring the brake pads into slight contact with the rotors. That apparently helps to keep the rotors dry in case the brakes needed.
  • You describe the problem very well. I have a 2006 Prius with VSC and I have the same problem on braking - hit a dip or rough spot in the road and the car stutters, the VSC light flashes, and I feel a lack of control for a second or two. I have not had the acceleration problem. I have not had this issue with any other car.
  • seldenselden Posts: 22
    I cannot accept that ABS will ALWAYS extend your stopping distance. In perfect conditions, yes, but in conditions of marginal traction, ABS is almost always going to work better. For an extreme (but not unrealistic) example, imagine going down a road where the left side of your lane is icy, and the right side is clear. Hit the brakes with ABS, and the wheels on the left side will pulse, while the brakes on the wheels on the right side will apply full force, something that is completely impossible to do without ABS. I have no experience with Jeeps, but depending on road conditions, applying the emergency brake while also trying to stop quickly can be an invitation to spin; in fact, that is exactly what I do to destabilized a car when I go out to practice driving on ice or snow (in an empty parking lot).
  • wwestwwest Posts: 10,706
    "..will apply full force.."


    Talk about "torque" stearing...!!!

    In the situation you describe, disparate braking traction right vs left, there is a design aspect of ABS (and VSC) that prevents the wheel on the higher traction side from applying an inordinant level of braking vs the opposite wheel. To do so might result in the car skidding out of control in the direction of the high traction braking.

    In the very same situation, WITHOUT ABS, I can apply "full' braking, and stear (something ABS [VSC] cannot yet do) counter to the skid to maintain a straight line.
  • revitrevit Posts: 476
    The Next Latest to Toyota Comes Next Week:

    By DEE-ANN DURBIN AP Auto Writer
    DETROIT February 6, 2010 (AP)

    Toyota has told dealers it's preparing a plan to repair the brakes on thousands of hybrid Prius cars in the U.S.

    In a message sent Friday night to dealers, a Toyota group vice president, Bob Carter, said the company is working on a plan and will disclose more details early next week. More than 100 drivers of 2010 Prius cars have complained that their brakes seemed to fail momentarily when they were driving on bumpy roads. The U.S. government says the problem is suspected in four crashes and two minor injuries.

    Public awareness of the problem "has prompted considerable customer concern, speculation, and media attention due to the significance of the Prius image," Carter said in the e-mail. "We want to assure our dealers that we are moving rapidly to provide a solution for your existing customers."
  • wwestwwest Posts: 10,706
    "..destabilized a car.."

    You're miss-quoting somewhat, if your intention is to "destabilize" you apply the rear parking brake AND crank the stearing hard one way or another. Otherwise applying the parking brake might well result only in your coming to a slow and STRAIGHT stop.

    Back in my wintertime days in MT I often found myself using the parking brake slightly, judiciously, to maintain a straight line going down a slippery roadbed slope. Nowadays ABS would undoubtedly make that a bit easier.
  • wwestwwest Posts: 10,706
    "..if one could hold brakes close to the loss of traction point.."

    If we could INDIVIDUALLY hold brakes...

    Yes, that would be "true" threshold braking, using the UTMOST benefit of whatever level of roadbed traction exists SOLELY for bringing the vehicle to a stop or to a lower speed. Should an inexpensive or cost-justified anti-skid control system (CVB, Continuously Variable Braking) ever be developed it could be used to provide true threshold braking AND stearing. Available traction allocated FULLY and SOLELY to stopping or slowing UNLESS VSC indicates otherwise.

    In the meantime...
  • It is a common mis-conception to think ABS improves stopping performance. (It will perhaps be better when compared to an all-out panic stop when all four wheels are locked up by the driver --- this is not really good driving and a lighter foot on the brakes will always outperform ABS)

    ABS is primarily intended to maintain directiional control in an emergency braking situation and it does this BY PERIODICALLY REMOVING ALL BRAKING FORCE to allow tires to periodically regain their grip on the road surface. Since you don't have braking force all the time you can't stop as well as you could if you could properly control the brake force yourself.

    ABS induced extended stopping distances are particularly noticeable on snow, ice and gravel --- just when you need optimum stopping ability. The problem is so pronounced that off-road vehicles often have an "ABS OFF Switch" to make off-roading in mud, sand, snow, icy and hills much safer.

    The 2010 Toyota Tacoma manual covers this on page 195 under "CAUTION' which states "Stopping distance when the ABS is operating will exceed that of normal conditions" and "The ABS is not designed to shorten the vehicle's stopping distance."

    There should be similiar warnings in your owner's manual.

    Hope this helps.
  • Lots of talk about Toyotas, but I have the exact same brake problem with my Acrua RSX (2006). It's my first car with ABS, so I thought it may be "normal" for the brake pedal to vibrate violently when braking hard and passing over a bump or rough spot in the road. Can't get hold of anyone to voice my concerns. This problem may be more widespread than just with the Prius. It's possible that most people in normal driving would never experience the problem. But if you're approaching a green traffic light that suddenly turns red and you hit the brakes hard while going over a rough spot in the street, you'll wonder if your brakes will ever take hold of the calipers.
  • wwestwwest Posts: 10,706


    If ABS detects impending lockup of any wheel due to braking forces it will FULLY release brake fluid pressure from that wheel's brake caliper just long enough, 10's of milliseconds, to alleviate the issue of the wheel actually coming to a full stop. That almost never requires removal of all braking force, "full" retraction of the brake piston.

    Think of it as PWM, Pulse Width Modulation, of brake fluid pressure, in order to "mechanically" maintain an "average" braking force.

    Most "off-road" vehicles will automatically disable ABS and VSC when the center diff'l is locked.
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