Prius Brake Problem - CONFIRMED BY TECH

Discussion in 'Gen 2 Prius Main Forum' started by grinthock, Feb 3, 2010.

  1. F8L

    F8L Protecting Habitat & AG Lands

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    We also do not have a long list of "accidents" that were the direct result of this feeling.
     
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  2. jsgreenfield

    jsgreenfield New Member

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  3. not1ie

    not1ie New Member

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    I live in Ireland and have a 2008 Prius that has the same brake issues. Brought it to the dealer, they said that there is no fix but they knew of the problem as one of the mechanics drives a Prius.

    They passed it onto Toyota Ireland who sent an expert out to look at the car.

    He said there was nothing wrong with the car, before even looking at it, he then proceeded to kick the tyres and blame them as they aren't the original Bridgestone tyres. So they also blamed my driving and that the car is perfect.

    The problem has lessoned after I fitted the different tyres, but the condition still persists over bumps, potholes or any uneven surface when braking hard or gently. Happens mostly when trying to use as much regen under braking. The car actually feels like it accelerates.

    There is one pothole on the main street in the village (downhill) that the car does actually accelerate, which is only metres from a pedestrian crossing. The road is very narrow for 2 cars to pass because of parked cars on either side of the road. So there is effectively no way to avoid it. So now I have to slow right down to crawling pace to avoid it.

    This doesn't happen in any other car I have ever driven. My wife's Nissan doesn't do it, my mothers Ford and my fathers Toyota don't do it.

    I drive for work and the car has 50,000miles on it and it was bought in July '08. I also work part time as a racing instructor and have a background in racing cars and engineering. I have driven extensively in North America (coast to coast several times) and Europe. So to say I have a lot of experience with cars for my early 30's then I don't think that would be an exaggeration.

    I have no confidence in my Prius at all now and Toyota Ireland refuse to acknowledge the problem, Toyota Europe refer me back to Toyota Ireland which is just an import company that buys from Toyota Europe and isn't anything to do with Toyota as far as I understand.

    I even looked at buying the new Prius to get rid of my problem car, but the new one still has the same issue from what some people within Toyota have told me off the record.

    So the car will be out of warranty in 13,000miles, so they are just stalling the problem until the cars are out of warranty and then it isn't their problem anymore.

    So I do feel for everyone experiencing the pain and I wish Toyota could just fix it, even if it was on the quiet then I wouldn't care; once it was fixed.
     
  4. qbee42

    qbee42 My other car is a boat

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    I will give you the fact that the car *feels* like it accelerates, but I can tell you with certainty that it doesn't actually accelerate. The laws of physics are not that easy to break.

    Tom
     
  5. BAllanJ

    BAllanJ Active Member

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    Well to be fair, he did say it was downhill, so it may have accelerated, but blame gravity not Toyota.
     
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  6. not1ie

    not1ie New Member

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    Yeah depending on the speed when I hit it then the speedo increases 1-2kmh. I only get to check the speedo at night as it is a busy main street and it would be far too dangerous to be watching the speedo when there are lots of people around.

    And no I am not releasing the pedal in panic or anything else. The pedal position is pressed down firmer when it happens which in itself gives a sudden braking force when the brakes start slowing the car again.

    The hill isn't that steep but when you are using the brakes then it is generally the idea that you slow down. The speed limit there is 50kmh but now I only pass there at 20kmh at most now. Happens every single time. It also happens whenever I am braking and the yellow warning lights flashes, but the yellow warning light doesn't always flash when it happens.

    Something in the computers seem to be confused/computing information for a split second before they act. Maybe there is an extra computer in the loop or something that has to process the information and then pass it on to another computer that is causing the delay/hiccup with the system.
    And as with most of the other reports it is after the pothole that the braking force goes out not actually when the car hits it.

    For my 2 cents, I believe it is something to do with the regen brakes cutting out due to ABS/EBD/TC or whatever system is detecting the problem and then there is a delay in the series of computers before the friction brakes kick it.

    Until Toyota can confirm that is the case then I am not confident that the friction brakes will come into play everytime. Or that it won't happen in an emergency stop, when that is the time you need are most likely need ABS/EBD/TC.

    Toyota Ireland may be happy with what they told me before even viewing the car, that "the car is operating as per Toyota specification". Read into that as you will.
     
  7. Qlara

    Qlara New Member

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    You've the wrong expectation already. In an emergency stop, none of these acronyms will help you stop faster/shorter. They can only help you stop straighter OR give you more control to the emergency avoidance in steering only.

    You should do some *safe, traffic-allowed* practicing in the super-panic stop situation and get familiar on the actual distance your Prius will need to stop-still in such condition. Every car has different traits in panic-stop distance and it's the only way to confirm your expectation of what your Prius can do in such emergency, not from Toyota's verbal speaking.
     
  8. Mike Dimmick

    Mike Dimmick Active Member

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    If the yellow light flashes, ABS has come into play. The described problem on the third-generation car was that ABS did not engage in this situation (lock-up causes transition from regen to friction braking). The software fix changes the parameters for ABS so they match the parameters for the transition to friction braking here, so that it should always engage ABS if it has to cut regen.

    The other part of the fix was to change the assumed braking coefficient of the friction brakes so that a more-likely-correct brake force is initially applied. This can never be totally accurate while the car is only measuring the pressure in the wheel cylinder, and extrapolating from there, and not the actual retardation force.

    Since you're having trouble when the ABS light doesn't illuminate, I'd start by assuming that there's something mechanically wrong with the friction braking part of the system - that the car is correctly applying hydraulic pressure but that it doesn't actually slow down to the expected degree. Troubleshoot this problem in the same way as you'd troubleshoot poor braking on a conventional car. The service manual says, for 'Hard pedal but brake inefficient', to check the following:

    1. Brake pedal (Out of adjustment, faulty)
    2. Front brake piston (Frozen)
    3. Rear brake wheel cylinder piston (Frozen)
    4. Front brake pad (Cracked, distorted, glazed or oily)
    5. Rear brake lining (Cracked, distorted, glazed or oily)
    6. Disc (Oily)
    7. Push rod (Out of adjustment)

    (This is the US manual, where the car has rear drums rather than discs, so substitute 'pad' for 'lining'.)

    Basically, check that the pad surface is good - not scored, glazed, and contacts the disc evenly. If not, replace. It's also possible to sand off glazing. Pads can glaze with heavy braking events (whenever the pad gets too hot and the surface melts), particularly if they weren't properly bedded in. Also check that the pads both sides of the disc move smoothly and freely on their slide pins.
     
  9. not1ie

    not1ie New Member

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    My only expectations of the brakes is that they work when I press the pedal.
    The problem here is that under normal braking conditions whether the road is wet or dry, if the car hits a bump or pothole that the car looses braking force for a second or so, as the car decides what to do.
    At 30mph you would travel 44 feet. That is a long distance.

    I think the problem is when the regenerative braking is active and the ABS, TRC or EBD activated; they cut out the regen braking and there is processing time and then activation time for the friction brakes to start working.
    The car got serviced on Saturday and they checked the entire braking system again for me. The pads have done 47,000miles and still have plenty of life left in them. So that may show how much I use the regenerative brakes over the friction brakes.

    I do believe that it is a design issue rather than a car specific problem and it is only showing up with certain driving styles.

    The ABS/TRC/EBD is really aggressive and the regenerative braking should be able to be modulated rather than just shut off completely.
     
  10. not1ie

    not1ie New Member

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    I was searching the net to see how many other people may have had the same issue with brake hesitation.
    I found a lot of complaints on the aboutautomobile.com website under customer complaints, you can search by year, make, model. I just looked at the 2007 & 2008 and there are a lot of very similar reports.
    It does seem to be fairly common occurance.

    I am still awaiting Toyota Ireland's and Toyota Europe's responses as to what they will do, since the car is operating within Toyota Specification.
     
  11. qbee42

    qbee42 My other car is a boat

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    They won't do anything. As you said, the car is working as designed.

    Tom
     
  12. not1ie

    not1ie New Member

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    I know there is little chance of them actually doing anything but I am not giving up.

    So far they have just insulted me and crashed my car, so I wouldn't call that customer service.

    So ever the optimist, I will keep bugging them until I get an admission that there is a problem or until they give me a large discount off a 3rd Generation Prius which has the problem fixed.
     
  13. F8L

    F8L Protecting Habitat & AG Lands

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    The fix for the GenIII Prius puts the "delay in braking" in line with the GenII Prius or so I've heard. Have you test driven a GenIII or the notorious pothole you mentioned in your other post? It would be interesting to see if there was a marked difference. :)
     
  14. a_gray_prius

    a_gray_prius Rare Non-Old-Blowhard Priuschat Member

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    If it were not such a boondoggle of situation for you, I'd say that this was kind of funny. Good luck, you'll need it (judging from my experiences with US Toyota service). :focus:
     
  15. not1ie

    not1ie New Member

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    There is a pothole/manhole cover just up around the corner from the dealer that their mechanics Gen II, my car and the fixed Gen III car all do similar things. It isn't as bad as the pothole in my village and it doesn't affect any other car that I have driven over it.
    To give you an idea, I can cycle over that same pothole/manhole cover on my hard tail bike and I don't have to get out of my seat; so it is not deep or severe.
    The Gen III car is better after the fix but you can still feel the brake hesitation but I would say it reacts in a fraction of the time that it takes the Gen II, and the skid light doesn't light up either as it does in the Gen II. Before the fix the Gen III was worse than the Gen II from what I've been told.
    The fix in the Gen III from what I understand is that the time lag (processing time) has been speeded up. It is just a software patch.
    The fix for the Gen II could be as simple as adjusting the traction control/ABS sensor so that it doesn't trip as quickly or a similar patch.
    That is if they are interested in doing it.
     
  16. not1ie

    not1ie New Member

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    Toyota Irelands only solution to the complaint is to get an independent assessor (who they pay) will examine the car and as they say will find the brakes work. How many assessors out there will be familiar with Hybrids? Very few.

    I saw on another website that a guy who owns '10 Prius bought an accelerometer to measure the length of time, he measures 0.8seconds or 800milliseconds where the car doesn't slow down when it is transitioning from regen to frcition braking.
    That is fairly consistent with all the reports I have read.

    So at 30mph you would travel 35feet in 0.8seconds. That is 2 car lengths, someone tell me that isn't dangerous please even if it is Toyota specification.
     
  17. apriusfan

    apriusfan New Member

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    The problem for owners is that absent a safety 'defect' (meaning the car's brakes fail under certain circumstances), in the U.S. (and probably elsewhere, too), there is nothing to compel Toyota to fix the drop-out. You have to just suck it up and either sell the car and move on or keep the car with the brake drop-out. Nothing like a middle-fingered wave is there?
     
  18. F8L

    F8L Protecting Habitat & AG Lands

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    I don't recall seeing many accidents that stem from this problem so how big of an issue is it? In most cases, you will be traveling at less than 30mph when this occurs anyway. <shrug>
     
  19. qbee42

    qbee42 My other car is a boat

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    The general experience expressed here on PC is that the drop out occurs during mild braking. When you brake heavily the Prius has already transitioned to friction brakes, so the drop out doesn't occur. I think this explains why we haven't seen a rash of accidents.

    Tom
     
  20. dboy

    dboy Junior Member

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    No, that's wrong. My Prius II has the bumpy brake problem, and I experience it every workday now. I got a new job in October, and there are several spots on the commute where I can replicate the problem 9 out of ten times. There's no ignorance or greed involved in my statement. Just simple observation, and an unsettling feeling when it happens.
    When the anti-slip control (not ABS) is activated while regeneratively braking over a bump, the ecu must be stepping in to tell one of the M engines to not apply so much force. I'd guess the ABS is completely uninvolved at that point.
    Good ABS, which I'm convinced my Prius has, can react in milliseconds not several tenths of a second, can apply the change to any of the four wheels, and is known for preventing, not causing this kind of problem.
    I'd further guess that if you emergency braked over the bumps, the problem would not occur because then the excellent ABS system would handle it.
    A deer bounding into the road has caused me to use the ABS on two separate occasions, once in the middle of a somewhat bumpy turn and once on a slick downhill that was wet after a long dry spell and it was flawless in both. I am grateful for the ABS system's exemplary performance.
     
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