Prius Sudden Acceleration: Much Ado About Nothing?

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Wrecked Toyota Prius owned by Elizabeth James, photo by Ted James, from Houston Press

Wrecked Toyota Prius owned by Elizabeth James, photo by Ted James, from Houston Press

So-called "sudden acceleration" has floated around the automotive world since it burst onto the scene in 1986. Now the Toyota Prius has become the latest vehicle in which the syndrome is alleged.

But like every other vehicle accused of speeding up without warning, no conclusive evidence of a systematic or repeatable problem has been uncovered--despite dramatic photos of wrecked Priuses, and even one of a Prius in a rushing river.

It started last month, when a lengthy article in the Houston Press entitled "Wild Rides" amassed several instances in which Prius owners allege that their cars stalled, accelerated wildly, or failed to respond to their brakes.

It's an odd article, with accident anecdotes, discussions of hyper-miling, and quotes from Toyota dealers about how hard it is to sell Priuses when gas is cheap. It even name-drops Hollywood celebrities like Leonardo DiCaprio and Cameron Diaz who own Priuses.

But a look at the data on the supposed sudden acceleration, including research posted by members of the popular PriusChat forum, paints a different picture.

Three main points counter the allegation that the Prius has a tendency to accelerate out of control, endangering its drivers.

(1) Proportionally, complaints about the Prius occur no more often than for other vehicles.

If you look up vehicles through the NHTSA's Office of Defect Investigation, you'll note that complaints of injuries due to "speed control" issues are recorded for more than 100 separate models. For the 2005 Toyota Prius owned by PriusChat member CHogan2, the data show 10 complaints and one injury logged, from a population of about 85,000 Priuses sold that year. Statistically, that's low enough to be considered "noise level".

CHogan2 then downloaded and tabulated all complaints related to vehicle speed control for the 2004-2009 Toyota Prius, which ranked only 18th in reported injuries. That's roughly consistent with the number of Priuses sold as a proportion of overall new cars.

(2) No vehicle can out-accelerate its brakes.

All cars are designed so the brakes are powerful enough to stop the car under its maximum engine power. In other words, flooring the acclerator and the brake pedal brings the car to a halt. And for more than 30 years, cars have been fitted with redundant dual braking systems, so that if one set of brake pipes loses pressure, the other will stop the car.

Assertions in the article, like the one from Prius owner Bobette Riner that she "pushed on the brakes but they were dead," are not technically credible.

(3)  "Sudden acceleration" has never been proven in any vehicle.

Reports of sudden acceleration rise substantially every time stories appear about the syndrome, but the first and most famous such allegation--in a 1986 segment on "60 Minutes" dealing with the Audi 5000--was ultimately traced to driver error.

Safety experts suggest that increasingly distracted drivers--Ms. Reiner admits she constantly watched the central monitor in her Prius to maximize gas mileage--may not be aware of their speed, and can even press the accelerator thinking it is the brake pedal.


Given the history of "sudden acceleration," the lack of any provable defect, and the predictable number of complaints, it's hard to conclude that there's any problem.

Or as PriusChat member Miscrms puts it, For the throttle control computer and hydraulic brakes to both fail all of a sudden and then magically fix themselves a few minutes later is basically impossible. One is an electrical system and the other is mechanical. They are independent. This is no more possible than both your mechanically-linked-but-computer-controlled fuel-injection system throttle sticking open and your hydraulic brakes failing in any "normal" car.

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Comments (70)
  1. Well I just got a 2010 Prius and during the first week I have had 3 separate incidents of non-threatening sudden acceleration. In each instance, I hit a bump in the road and the car instantly started to accelerate. Pressing the break immediately slows it down but there is certainly a problem. Today when it happened I noticed that the losing traction warning light came on and stayed on even when the car was at a stop. The light went away when I turned off and on the car. Definitely a problem.

  2. Had same behavior today - while braking, hit a bump, car started to accelerate. Brakes did overpower the engine and stop ok, but engine definitely accelerated after the bump despite my foot being on brake, not gas.

  3. "All cars are designed so the brakes are powerful enough to stop the car under its maximum engine power."
    Not true. My wife accidently drove our car 20 miles on the freeway with the Emergency Brake engaged. Destroyed the brakes but the car travelled normal freeway speeds.
    Over the weekend a family was killed in their Lexus when it accelerated to over 100MPH before coming to the end of the road and crashing. The incident lasted long enough that one of the occupants had time to make a 911 cell call describing the situation.
    The driver was a 19 year CHP veteran. Not likely to accidently step on the gas for several strait minutes.
    And the floor mat excuse is BS. Their are reports of this happening with the floor mats removed.

  4. Damn, you should have got the Advanced Technology Pkg. w/ DRCC and LKA. But you know you guys are right, something is wrong with the Prius 2010. When I was driving at 45-50 mph, I suddenly hit the gas, and upon reaching 70, the cars front end began to lift, and the next thing I knew, I was flying. I got to 35,000, did a few barrel rolls, and landed.

  5. Sudden Acceleration is a serious problem in all cars, not just Toyotas. That said, point #1 above is true. The other two points are, however, false or at least misleading. As pointed out in the previous post, it is very possible for a car to out-accelerate its brakes. You can see evidence of that in Dateline's investigation of S/A (posted on YouTube and The third point is misleading because S/A is caused by electronic malfunctions in the throttle control. Unfortunately, this type of malfunction does not leave behind evidence. This is why car companies have been able to avoid liability in S/A cases for so long.

  6. I just came home from a 7 hour trip in my 2009 prius. I have about 6000 miles on my car. I had a sudden acceleration occur....I know I was trying to stop the car with the brake.....finally just hit the power button...I checked the mat and there was no problem. I am very concerned!!!!! I drove another 1/2 hour....pretty nervous but it didn't happen again.......but worry that it will happen without warning and I may not be so lucky. How will the service department recognize the problem if there is no tell tale sign?????

  7. All city cars are very dangerous! Toyota Prius

  8. Dude,
    wow - you are so sure it can't happen that you made toyota to RECALL 3.8 million vehicles. Way to go!!!

  9. The Prius is a useless vehicle anyways. They should just refund all the owners, or just allow them to be traded in for VW TDI's. The TDI is cleaner for the environment, cheaper AND more fuel efficient. I pity the fools that got sucked into the Prius hype.

  10. I found this article because I was searching to see if anyone had been experiencing the same problem I have, which is exactly what the first poster--Steve Glauberman--describes. My 2010 Prius often accelerates as I am going down hill and braking. I also have the feeling of hitting a bump when it happens, although I'm not certain if there is an actual bump that I'm hitting or if it's made by the car itself. My brakes easily over-power the acceleration, but it happens a lot. I love my Prius, but I don't love that it accelerates by itself, especially as it often happens as I'm slowing down at a stop light.

  11. How could Toyota not include this simple safety override into their "drive-by-wire" system (when the Germans certainly did.....)?! And how could any such system be officially approved and certified without it by any manufacturer?!
    October 7, 2000
    Smart Gas Pedals May Solve Floor-Mat Problem
    By Christopher Jensen
    Some automakers – primarily European — are using an unusual method to reduce the chances of unintended acceleration from something like a floor mat getting tangled up with the accelerator: smart gas pedals.
    If the vehicle is moving and both the gas and brake pedal are being pushed at the same time the computer tells the engine to ignore the gas pedal.
    “It is an additional safety feature,” said Thomas Plucinsky, a BMW spokesman. “The brake takes precedence.”

  12. I experience this for the first time the day I purchased my 2010 Prius. It only happens after I've hit a bump and it is a definite acceleration. I've spoken to the dealer and they've said they've NEVER heard this happening in ANY car.

  13. I'm having the same mini-sudden acceleration issue with my 2010 Prius. Seems most often to happen going over manhole covers - bump + slippery surface. Also sometimes happens when I'm slowing to a stop (almost rammed the car in front of me) and going over big bumps (like speed bumps). The same thing has happened in other Priuses I've driven (i used to be part of I-Go, the non-profit equivalent of Zipcar). In fact, I've now driven probably 5-6 different priuses and have experienced this in almost every one of them.
    How do we get Toyota to listen?
    Voelker, do you have any advice? Even if you believe the Priuses are perfect, surely you support the honest sharing of information and experience.

  14. I have a 2005 prius and know what you mean when hitting bumps. I experience this on only one section of rippled pavement, but it always stopped. One thing people may not believe is the energy potential of the electric motor, while they are slow to start once they are turning the inertia can be very great. It is my opinion, if there were a severe malfunction the electrics might overcome the brakes at higher speed.

  15. You sad wanker. People are dying from this. I hope you remember them when the cause of this is uncovered and you are proven very very wrong.

  16. to kellyj
    emergency brake operate differently
    you better learn more about a car before you drive.

  17. I have had the same exact problem described here. I hit a bump or a manhole cover and the car accelerates. I am taking it back! Can I take it back?

  18. Years ago I owned a 1985 Audi 5000 and I DID experience sudden accelaration. official final 60 Minutes brought enough attention to the problem which over the years resulted in the 'have to depress brake pedal before putting in drive'. I am a mechanic and my take on the problem was an over-zealous idle compensator integrated into the old Bosch fuel injection system. If the engine stumbled, the compensator would essentially step on the gas. Not good if you are three feet from the garage wall with somebody standing in front of you! Anyways,25 years later my daughter buys a 2010 Prius and guess what...."daddy my car is accelerating". My 'no engineering degree' take on this one is that with all of the systems interacting in this car is that maybe,just maybe, it has something to do with the dynamic braking interface with the anti-lock braking system. If the dynamic braking is engaged,it helps slow the car down. If you hit a bump, this could possibly start to engage the anti-lock braking system. I would think that any momentary dis-engagement of of the dynamic braking could, in a sense ,let off the brakes without you knowing it giving you the sense of acceleration.I don't know if this is even possible. Probably the only differance in the repair to the Toyota as opposed to the Audi is that they will have to make a software change instead of turning a screw. Of course that is if this problem really exists!

  19. Sorry didn't know I was limited to 1500 characters.Anyway can anybody tell me if this is real acceleration or just a sense of acceleration due to a interuption in braking? Has anyone seen the tach when this happens. Does the episode last long enough to get a sense of weather the engine actually increases rpms? I have felt some pretty odd behaviors of antilock brakes over the years. Somebody at another site made a point that anybody has this problem shoul post to maybe get Toyota's attention. My daughter has a friend with the same first name having the same issue with her 2010 Prius. So I guess maybe people named Melissa shouldn't own a Prius....That might be the whole problem!! So much for sarcasm. I obviously have a concern over my daughters safety, so please post!

  20. There is a solution for this very real and deadly problem.

  21. I have also experienced this suden acceleration in my 2010 Prius while braking. It has happened 6-8 times over the past 6 months. The service department has said "We've never heard of that before". Of course it could not be replicated as this happens infrequently..although I also have almost hit the car in front of me. Your comments have been very helpful as it does appear to happen when I first apply the brakes and there is an irregular raod service or a manhole cover. I have contacted Toyota National about the problem and am wondering if anyone has had the problem diagnosed and fixed?

  22. I've had the same experience with our 2010 Prius. My Prius hit a bump during wet conditions, and it accelerated on it's own. The break does stop the car, but it's very scary and you feel like you're not in control for a second. This has happened twice to me and we've only owned it for 1 1/2 months so far.

  23. I've had the same experience described by everyone else with our 2010 Prius. It doesn't happen every time, but often enough. When I run over a pothole as I'm braking (which unfortunately are numerous and impossible to avoid in LA), my Prius accelerates for a couple of seconds which can be scary due to amount of traffic where we live. I have yet to drive in the rain, but I can only imagine the lack of control to be worse.

  24. I have exactly the same issue with a surge of acceleration as I come to a gentle stop on bumpy pavement. It happens often enough that I have learned to anticipate where it happens on my regular driving routes.
    I have a 2010 and am wondering why they are not included in the recall. I am not interested in having my brakepedal clipped, but would like the software fix that allows braking to override acceleration. Does leaving the 2010 out of the recall mean that this already exists in my car? Somehow I doubt it.

  25. I posted #18 & #19. Can anybody answer if the engine really accelerates or intermittant braking due to anti-lock brakes makes you feel like your are accelerating? Also when you talk to your Toyata dealers,Please tell them to look at this website!! This is important. If you think that Toyota will admit to this problem, you are very naive. Only non-stop pressure,diligence with documentation,and usually(unfortunately)a serious accident, will get action. From the number of posts, this is a real problem. Please keep up the pressure with your dealer until they are tired of hearing from you.

  26. I have a 2009 Prius, have had only minor problems, one on a very icy road, but I'm getting very nervous about driving my car & won't drive with my granddaughter in it, or let anyone else drive it. I want to trade it in for a safer hybrid, hopefully a hatchback. Any ideas?

  27. I own 2009 prius. so for i am still alive but if you read in the comments later that a ROSS as die, it will probably be, because my accerating problem, braking problem and car dieing at 76 mph and droping speed from 76 mph 61 mph instantly and jerking servely to the right and toyota not doing anything about it. I am retaing me a lawyer now to see if he can do something about it.

  28. I have owned my Prius 2010 since Aug. '09 and have now experienced the acceleration while breaking on two different occasions. It does get my adrenaline pumping when it has happened. I've also had the "traction assist" light come on while sitting at a stop light. After owning Toyotas for 30 years, this has me nervous.

  29. I have this problem too - told the dealer about it in Santa Monica, CA -
    They at least acted like they never heard of it and weren't able to recreate it...but it's quite real. It is definitely an issue with the 2010 model and more than anything it can be quite a freak out when it happens. I thought it was only happening to me but clearly it's out there.

  30. If all car brand have cases like these then the one thing that i would look into would be my car insurance. Make sure you are covered for all things that the manufacturer is to blame for so that you dont have to pay it yourself.

  31. My 2010 Prius often "accelarates" when I go over train tracks, bumps in the road, man hole covers, etc. It doesn't happen every day, but at least a couple of times a week and I only drive about 200 miles a week. I haven't reported it to the dealer because I feel like they won't be any help. I feel like it could easily cause an accident.

  32. My 2010 Prius often accelerates while going over rough pavement, bumps in road, etc. also. The dealer said they never heard of this before. I don't believe them. I like my Prius, but I want Toyota to be up front about this - there is something going on. I would like to build a network of people with the same problem to share experiences. I would like to approach Toyota with some meat (many people with the problem). We cannot all be hallucinating. Please e-mail me at with contact information. Thanks.

  33. Having driven a Prius for about 150K miles, I can say this stuff about the car "accelerating" over bumps is not right. Yes, there is a sensation of that, but it is not acceleration, nor is it a problem. Normally, the braking is handled by regeneration. There are mechanical brakes for backup. When a wheel slips, activating the anti-lock brakes, as it does when driving over a bump, the braking changes over to pure mechanical brakes. What you feel is the momentary handoff. The sensation lasts about a tenth of a second.
    That is all it is, nothing to worry about. This is a totally different thing than "sudden acceleration" that you read about on the news.

  34. There is a definite problem with the Prius and Toyota refuses to address it, still standing by the floor mat recall for Prius (even though all other cars are in the new recall). I was driving on open highway (thank God) with the cruise control engaged. I accelerated with the cruise still on, to pass a vehicle, after taking my foot off the accelerator, the car continued to accelerate quickly reaching 93 MPH. I tapped the brake to disengage the cruise and it did not do so...I braked harder, still with no results and continuing acceleration.... I manually disengaged the cruise using the button...and the vehicle finally slowed. Fortunately I was on open highway unlike others that have had this occur. BTW my floor mats have the anchors installed-it was NOT a floor mat issue, nor did the pedal stick. This was an electronic control problem.

  35. Why was the Prius not recalled also? Like azcoolmom, the 2009 Prius touring model cruise control was set at 65 mph and I accelerated to pass. The car kept accelerating to over 90 mph, unresponsive to braking. It slowed only after turning off the engine. This happened THREE times Sept/Oct 09. NO floor mats! Dealer "found nothing wrong" at that time. NTSB report filed without response.
    Will it take the death of a Prius owner also to add this car to the recall?
    I suggest that EVERY Prius owner w/ this problem NEEDS to file a NTSB report so we can get added to the recall.

  36. I guess it is now proven that this so-called Car Expert didn't really know shit. Toyota has admitted the problem. Also Good Morning America tested brake with full acceleration which showed that "Brakes will not stop most vehicles under full acceleration once they're already moving." So please stop writing nonsense article like this before you get people killed.

  37. as people have mentioned i have a 2010 prius that has the same problem of hitting a large bump and the car accelerating. a friend of mine also has said he has the same problem and can duplicate it. dealer service manager called toyota engineers after i sent him this web page and toyota has acknowledged the problem and believes it is in the software when the car is switching over the ABS override. i encourage all with the problem to file a complaint to the NHTSA to get toyota moving quicker

  38. I too have a Prius and have experienced sudden acceleration after hitting a small bump in the road. It was a 40mph zone, near a high school and my car accelerated to almost 60mph before I could get it back under control. I could have been another Toyota death statistic.
    Even CNET reports that Steve Wozniak (Apple Co-Founder) has experienced sudden threatening acceleration on his Prius. (CNET:

  39. Great idea contacting the NHTSA; however, Wozniak tried contacting the NHTSA and Toyota and both of them ignored him. So I doubt you'll get anywhere. I called my dealer to complain, and he argued with me that my Prius is not one of the "affected models".
    I would never let my wife or daughter drive this car. I am extra careful when I drive now, especially around school zones. Why can't Toyota, use the same software as the BMW and disable the gas pedal if someone hits the brakes?

  40. Attention Prius owners. I experience sudden acceleration and worse yet, temporary loss of brake function with my Prius when going over a pothole near my son's school. This is very worrying. I called my Dealer and they also told me my model is not affected by the recall and that it is within normal operating parameters. "Normal Operating Parameters"?? When your car loses its brakes?
    I suggest we all contact NHTSA. This problem will not get fixed unless they know about it. Contact page is here:

  41. Umm - why didn't the idiot turn the engine off? That would have slowed them down in a hurry. All this talk about acceleration unexepectedly is a load of garbage.
    By KellyJ
    #3, Posted: 8/31/2009
    "All cars are designed so the brakes are powerful enough to stop the car under its maximum engine power."
    Not true. My wife accidently drove our car 20 miles on the freeway with the Emergency Brake engaged. Destroyed the brakes but the car travelled normal freeway speeds.
    Over the weekend a family was killed in their Lexus when it accelerated to over 100MPH before coming to the end of the road and crashing. The incident lasted long enough that one of the occupants had time to make a 911 cell call describing the situation.
    The driver was a 19 year CHP veteran. Not likely to accidently step on the gas for several strait minutes.
    And the floor mat excuse is BS. Their are reports of this happening with the floor mats removed.

  42. Prius Owners: In the news just today. Toyota admits to antilock brake issues with the 2010 prius sold BEFORE late January 2010. There is no official recall yet, but hopefully soon as they fixed the models sold after late January. We are not making this up, our experiences are just now being validated. Why Toyota is only now admitting to this problem is concerning. Call and complain to your dealers today!

  43. DRIVE,SPEED,AND PRAY ,Screw the writer I Used too Work On Them.BEWARE

  44. Turn the car off? Won't that turn off the power steering, braking? Wouldn't turning the car off give the driver less control?

  45. #46 exactly what power steering are you talking about? Electric P/S, can still steer when switch is off only with increased effort.
    #42 When you go over a bump do you keep your foot on the gas?? That could explain it... #34 same thing.. try lifting your foot of the gas pedal when going over bumps.. #17 same thing..

  46. Got to expect some bias in this web site. It's owned by Jeff Birkeland who records indicate is VP of Hugh Gear Media which owns a number of web sites which receive advertising revenue from car companies.

  47. "Good Morning America tested brake with full acceleration which showed that "Brakes will not stop most vehicles under full acceleration once they're already moving." So please stop writing nonsense article like this before you get people killed."
    Though of course if the brakes don't work one is screwed but otherwise I'd rather trust Car & Driver's results than some hack morning show's test. Read it carefully and note the vehicles tested & methodes. This is reporting the testing of wide open throttle at highway speed against simultaneous braking to measure difference in stopping distance from just braking with no stuck trottle (normal):
    I'm not sure why that trooper didn't throw it in neutral or kill the engine (I'd rather drive on manual steering on the highway than rocket off the road at full speed).


  49. I drive a 1999 Toyota Camry and from the beginning have had the same problem of sudden acceleration after hitting bumps. Was also told by mechanics that they couldn't find a problem, so I compensate by driving slower on bumpy roads and leaving enough distance between my car and the one in front of me. In light of how widespread this problem seems to be, the contention by all these Toyota mechanics that they have "never heard about it before" is more disturbing than the problem itself.

  50. I can see the sensation you get when you go over a bounce and the brake system changes espeically if it has a flywheel that might reengage with no brake during the transition.
    However, what I am not getting is why no one is asking why they did not put it into neutral. The lady that testified to congress put it in reverse? The guy today finally turned it off. Both had time to make a phone call. More than enough time to put it into neutral or turn it off and back on which I would guess would return it to normal.
    Now at a stop sign or in traffic I can see this is a major problem but on the highway I just do not get it and driving off the road without turning the car off is just beyond my understanding.

  51. If this happens, why not put the car in neutral and then apply the brakes? The engine will rev, but it will not be in a gear and the brakes will stop the car. Once stopped, turn off the ignition.

  52. I love how people talk abot the RPMs going up to 3000... My 2008 Prius doesn't have a tachometer!!! Neither does my 2006... As far as I know, none of them do. But just because some people are full of crap, doesn't mean there isn't a problem. I've never had a problem on either of mine, and neither have my parents who have a 2010 Prius, but that's a pretty small sample set.
    I can understand how somebody could think that the traction control was causing a minor acceleration, because losing traction like that does make you feel like you've lost control. Which I guess you have at that point. But I have trouble believing that a lot of these complaints aren't legitimate.
    BTW, my Prius will not shift into neutral while it is moving. Nor will it turn off. These things have a power button, not a key. I also tried pressing the accelerator with my foot also on the brake, and it does rev the gas engine but doesn't have any effect on moving the car.
    So as much as I love my Priuses, I have to admit the drive-by-wire offers new opportunities for mistakes.

  53. Wow, all these sudden acceleration issues. I don't buy it, sorry guys. I've owned Toyotas for over 20 years and the only acceleration issue I have is, I can't get enough acceleration *lol*. Really? Come on you can't put your cars in neutral. You can't press and hold the power button for 3 seconds to turn off your car if in fact, you really did have a "sudden acceleration problem". LOL, give me a break some of you people are just claim staking. Learn how to drive, seriously. Oh, and please someone discredit this article, I really want someone to post a link to facts here, not just hear say chopped liver rumors. Because everything in this article is absolutely true.

  54. Funny how all of a sudden all this is happening. Not sure what to believe but for anyone just out for a buck from a Company with deep pockets, karma is going to kick your butt. I have to admit, some seems to be operator error just reading these posts. Can't wait for the truth to come out. Then we will all know!!!

  55. No knowledgeable automotive enthusiast or experienced mechanic would ever claim that a car's engine cannot override its braking ability. At full throttle at highway speed it's unlikely most cars would slow down in any reasonable period, while cars with actual horsepower(thus not including the Prius) certainly would not. In the case of Toyota, though, part of the issue is the brakes are electronically controlled as well, thus the only brakes actually available is the cable actuated parking brake on the rear wheels. Utterly useless.
    It's also worth noting US made cars have been equipped with dual reservoir master cylinders since around '64, and this does not make a difference in overall braking, only prevents complete system failure as opposed to either front or rear failure.

  56. Drive-by-wire FAIL!

  57. I found this post while researching the same problem.
    I have experienced this on three specific instances. All happened while decelerating with foot on the brake and hitting a bump on the road at the same time...the prius suddenly and unexpectedly accelerates but will respond to firmly pressing the break. It is disconcerting and can catch you by accidents yet, but one close call in traffic.
    I want to say, that on balance, I have been very pleased with this vehicle, but this is absolutely an issue and not due to some sort of internet driven hysteria.

  58. I still don't buy all this "sudden acceleration" problems. Me and several of my friends have been driving our Prius models since 2003, each of us having at least two models. None of us have ever had any acceleration problems and we laugh whenever we read that someone has. I especially like the one poster who said his Prius smashed through a wall *lol*! Come on guys, seriously? Funny how Toyota was the leader in reliability and safety and never had any problems up until 2010. Too Funny!! LOL! As the original author wrote, this is EXACTLY like how the Audi 5000 issue was back in the day. People were claiming a lot of bull... Just like how they use to say Rock music causes kids to worship satan, play D&D, an kill people. LMAO!

  59. Still stand behind your article? Seems there are a few people feeling strongly their experiences are quite legitimate.

  60. My 2008 Prius is at the dealer for a sudden acceleration incident. I’m a very careful driver and know that the car accelerated without any input. Conditions: 34 mph, road – straight, level and smooth, right foot just touching the gas pedal, cruise control off. The car went into full acceleration mode quicker than stomping the gas pedal or using resume on the cruise control. Once I realized what was happening, I pressed the brake pedal. The brakes worked perfectly. The problem did not repeat; drove car to dealer the following day (they wanted to tow it). Will update site when I know the results.

  61. Own a 2010 Prius - wife has 2007 Prius. I just had the ABS software upgrade yesterday on my 2010. Braking seems fine - the slight hesitation when slowing and going over a bump is gone. Perhaps they will come out with one for the 2009 and earlier models soon?

  62. The "sudden acceleration" when going over bumps, ripples, etc. is caused by the traction control system. Whenever the computer senses any kind of wheel slip it cuts the throttle momentarily then reapplies it rather ubruptly so it feels like it's lurching forward especially if one feels the car slow slightly and subconsciously gives it a little more "gas." This is merely bad traction control programming. I can get my 2008 Prius to do this at will. And guess what, my 2008 Honda Ridegline does the same thing. Modern parking (emergency) brake systems only apply the brakes to two wheels, usually the rears so that wouldn't stop a "runaway" car but applying the brakes normally should slow any car down. Try it sometime!

  63. Follow up to post on 3/15/2010. The dealer had the car for one week. They said that they were instructed by corporate to capture and send stored data from the onboard computers. Pictures of the gas pedal at various locations were photographed and sent. They were then instructed to instrument the vehicle and capture data during various driving situations. They drove the care for 35 miles. They paid $210 for the rental and put about $20 worth of gas in my car. The software was not changed and they did not change any hardware. So far, it has not repeated.

  64. My 2008 Prius accelerates probably 20% of the time when I hit the breaks over bumpy surface. This is my dream car, so I'm really not happy to think about having to sell it, but I don't want the risk.

  65. they are very good !!!

  66. they are very good and useful!!!

  67. I actually noticed this too. I was breaking and hit a bump and my car accelerated hard, I had to slam on the brakes to stop in time before hitting person in front of me. If I was a tailgaiter I would have hit them for sure. To me it makes perfect sense that this is a traction control system issue and I think all car companies (not just Toyota) should look into this issue and tweak the Traction Control Systems so it doesn't happen.

  68. All automobiles are developed so the brakes are potent adequate to cease the car under its highest engine power."
    Not accurate. My wife accidently drove our car 20 miles on the freeway with the Emergency Brake engaged. Destroyed the brakes however the automobile travelled usual freeway speeds.
    More than the weekend a loved ones was killed in their Lexus when it accelerated to over 100MPH before coming to the end with the road and crashing. The incident lasted extended adequate that a single with the occupants had time to make a 911 cell call describing the situation.
    The driver was a 19 year CHP veteran. Not likely to accidently step for the gas for several strait minutes.
    As well as the floor mat excuse is BS. Their are reports of this taking place with all the floor mats removed.

  69. My wife and I have our second PRIUS, and she recently experience a sudden acceleration (with our kids in the back) from standstill as soon as she turned on the car. High revs and the car surged about 10 feet, crashed into the car opposite and pushed it through the fence. Only stopped when she hit the off button. We raised this with Toyota, and they raised a case, sent out an assessor (after 6 weeks) and now are saying it is not their problem. We loved our Prius, but Toyota's handling of this, the stone-walling from customer care is dreadful. There are obiously problems, but they are not taking responsibility. No longer a happy Prius driver !!

  70. Not to pick nits, but most production cars with hydraulic brakes do not have "redundant" braking systems, but rather a split system that isolates pressure into two separate "circuits" so that a pressure loss in one does not immediately render the whole system inoperable (cars with 4-wheel ABS or traction control will split this further into a 4-channel system). A "blowout" in one circuit will still cause loss of brake function on whichever wheels are connected to it, and in fact will still provide a path for you to quickly pump all your brake fluid out after just a few stops.

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