By on August 13, 2007 has collected complaints from Toyota Prius owners regarding throttle control. One, a new Prius with 600 miles on the odometer, accelerated wildly while the owner was attempting to merge onto a busy interstate. On another occasion, the traction control system (itself another problem reported on the site) kicked in and the car accelerated. A third time the car refused to slow after passing another car. One Prius owner, an engineer, discovered that tapping the lever that disengages the cruise control solved the problem– even though the cruise control system was already turned off. Toyota denies any mechanical or software problem exists. They suggest that a wadded carpet may have caused a sticky go-pedal. 

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25 Comments on “Toyota Prius: Unintended Acceleration, Traction Control Problems and Throttle Failure or… Owner Error?...”

  • avatar

    Hmm, I think I remember that GM had this problem on the early Cavaliers. The cruise was never really “off”, and if you bumped the button while sitting at a stoplight the car took off.

    One of our driving instructors in high-school had a student total one of the cars this way. Hit the button at a stop-light and put it straight into a pole. That was the reason given anyway…

  • avatar

    Interesting. As a Prius owner, it’s always good to keep up on what the possible problems may be.

    Automobiles are extremely complex with obvious potential for problems – and so much more so, for the Prius and other highly complex hybrid vehicles.

    I find it extremely fascinating that there have been so FEW problems with the Prius and other hybrids.

    As I read recently with regards to aircraft engine manufacture, 99% perfect is not anything like “good enough”. 99.99999% might be getting close.

    Likewise hybrids. Overall, I’d say that with a highly enviable reliability record, the Prius is still one phenomenal car.

    But yep, stuff can go wrong. It’s good to know what the possibilities are.

  • avatar

    i’m just impressed that anyone got a prius to accelerate “wildly”

  • avatar

    Accelerated wildly? A Prius? I don’t think it has enough power for that description!

    Seriously though, this is probably another Audi 5000-type situation. Electronic glitches are common, but stupidity is even more common.

    jrlombard, I hope that student eventually learned that you can use this thing called “brakes” to slow down a car!

  • avatar

    If floor mats are this much of a problem, being blamed and/or causing actual problems (for Prius or a long list of other cars), how come no one has redesigned the little buggers?

  • avatar

    This car cannot have problems…. It’s a Toyota!!!

    Toyota has said it’s a wad of carpet??? Sounds like that one is out of GM’s playbook.

  • avatar

    No engine is powerful enough in a street car to over power the brakes. An engine in a Prius is not powerful enough to overpower much certainly including the brakes. Sounds like Audi all over again. Most likely driver error. Besides if someone hooked a laptop into it right after the incident you could get readouts on what all really went on most likely.

  • avatar

    The Audi 5000 situation got an excellent write-up on this very site:

  • avatar

    While I’m not a big fan of Toyota, it does strike me lately that any mention of a Toyota defect gets far more attention than defects by other manufacturers.

    The Tundra gets recalled due to a supplier problem and its big news. Meanwhile, F-150 smokers spew fire out the back and the media yawns.

  • avatar


    By now you should know that TTAC is an equal opportunity muckraker.

  • avatar

    Thhe Tundra gets recalled due to a supplier problem and its big news. Meanwhile, F-150 smokers spew fire out the back and the media yawns.

    They really didn’t yawn, so much as say, “Cool!” I mean, would you take your truck in to have them fix the world’s greatest anti-tailgating repellent?

  • avatar

    I thought car guys were all for afterburners.

  • avatar


    No engine is powerful enough in a street car to over power the brakes. An engine in a Prius is not powerful enough to overpower much certainly including the brakes.

    Yeah, but in a Prius the brakes generate the power for the engine so the harder you brake, the faster you can accelerate :) A bit like those computers in 60’s Sci-Fi movies that always blew up in positive feedback loops !

  • avatar

    I think it is horribly unsafe to be driving those vehicles.
    I give them a grand for each as a public service.

  • avatar
    P.J. McCombs

    A bit tired of the “slow-ass Prius” schtick, to be honest. 0-60 in 10-11.5 seconds (depending on whose test you read) is on par with most automatic-transmission economy cars.

    It’s a hopeless argument, but between the CVT and the electric motor, the Prius actually has a decent nudge of torque off the line compared to most slushbox econocars. Those who’ve driven one know what I’m talking about.

    Yes, the wife owns one, so you’re assuredly hearing sour grapes. I have noticed that the(undefeatable) traction control tends to nix brake force when you hit a bad pothole while slowing, creating the impression of unintended acceleration.

  • avatar

    I regularly blow the doors off “conventional” cars at the traffic light, just by driving hybrid-style in my Prius. You know, zip up to speed then back-off to obtain 50-99 mpg in town. (Lessen the amount of time you’re at 10 mpg under acceleration and you increase the amount of time you are at 50-99 mpg).

    While other folks are sitting there with 5000 pounds to move and their torque convertor is slowly spooling up, my electric motor has propelled me 1/2 way across the interection already.

    In fact, it’s caused me to be much more alert for idjits driving through red lights – despite side air bags, “anything” (including myself) can be squashed by some dang fool flying through a red light in a semi – or a Ford F250 with a 28′ boat behind it, for example.

    By the way, the Prius can beat the pants off virtually any 1970’s car built in Detroit 0-60 and the vast majority of US family cars built in the 1950’s and 1960’s. 0-60 in about 10 seconds was really fast going “back in the day” and represented about what you could expect from a 1960’s mid-sized V8 family car such as a Malibu.

    Just read an OLD road test of a 401 cubic inch AMC Matador from 1974 (police package) and it could only manage 0-60 in about 12 seconds. Just read an OLD road test of a “newly down-sized” 1978 Chevrolet Malibu with V8 and it could only manage 0-60 in 13.1 seconds.

    Maybe we’re a lot more spoiled than we realize, with our “demands” for 0-60 in 6 or 7 seconds, and 145 mph tops speeds in V6 mid-sized family cars.

  • avatar

    partsisparts- we have learned that all makes are very reliable and reliability is no longer a differentiator in the buying decision so it doesn’t matter that this is a toyota. Kia, Lexus, VW, reliability is not a factor anymore.

  • avatar

    P.J. and glenn, you’re taking this far too seriously! Nobody here said the Prius is exceptionally slow, but its acceleration is never going to give your passenger a rush either. The “wildly” description certainly is accurate, since the car is making decisions by itself and is therefore wild or “untamed”, but it also provides me with an amusing mental image of the Prius accelerating “wildly” while the driver calmly thinks, “hmmm, it seems to be accelerating by itself. I guess I should hit the brakes.” The same is true for any other car that takes over 10 seconds to get to 60 mph, and I do know there are a lot of them.

  • avatar

    OK rpn 453, I see your point. But can you see my point – what do we need to do 0-60 in 6 seconds in a family car for, or for that matter, why have a Hyundai Sonata V6 capable of 144 miles per hour? Because – it is.

    The baby in the baby chair in the back seat probably is going to sick up all over the place with repeated (or even one) high speed acceleration run, and if grandma’s in the car, she’s liable to crown the driver with her stick….

    I’m just sayin….. when is enough enough?

    I prefer to go fast in a go-fast car, on a track.

  • avatar

    Anybody who’s still trying to peddle the “sudden acceleration” myth has a long row to hoe. It’s been pretty much established since the Audi 5000 debacle that the problem is, ahem, “pedal misapplication,” as in “I was standing on the brakes, but the car just kept on going!” (foot firmly planted on gas pedal).

    As for cruise control, I know of none that operates below 25-30 mph, so if you hit “resume” while stopped after using cruise, the car won’t go anywhere (granted, the unit will “remember” your set speed after you get above 25-30, at least in domestic cars and some imports).

  • avatar

    It gets better, with the way the market is going, pretty soon they will be claiming unintended acceleration on their houses. Mostly south.

  • avatar

    One must first analyze the source of these reports. Consumer Affairs is a trolling net for anyone who may want to register a complaint, valid (or not) real (or not). To date there are very few complaints by real people with real VINs ( actual vehicles ) at the NHTSA site.

    The owners first sought out Consumer Affairs to lodge a complaint? I’m skeptical.

  • avatar

    I had my experience with prius yesterday, got stranded for 30 minutes in the nowhere, because car’s engines keep accelerating even with stop brakes, when I set on park and tried to drive – its’ contune drive like a crasy. After turned off for 20-30 minutes it started drive normal again. I am going to take today to check it.

  • avatar

    I read that they redesigned the braking systems for the 2010 Prius. That appears to be Toyota’s response to the fact that the U.S. Generation 2 Prius (2004-2009) has had low-speed brake failures reported to the National Highway Traffic Safety Administration (NHTSA) at 31 times the rate of such failures reported for the 2004-2009 Corolla, which of course has traditional brakes.

    Many of the Prius low speed brake failures were in low-speed city traffic, resulting in rear-end collisions without injury. It appears that the several computers that control the complex braking systems were too busy calculating the most efficient way to apply the brakes, and did not get around to actually applying them, until it was too late. Toyota never took responsibility for the problem, but the 2010 redesign indicates they were aware of it. Unfortunately, the NHTSA never initiated an investigation despite the extremely high rate of failures. The detailed failure reports (“complaints”) are available to the public on the NHTSA website.

    The details are these: Through March 2009, 2004-2009 Prius has received 44 complaints of low speed brake failure. 2004-2009 Corolla has received 7 complaints of such failures. Given that about five times more Corollas than Prius were sold during 2004-2009, 44/(7/5) = 31 times the rate of brake failure for the Generation 2 Prius. Let’s hope the 2010’s brakes work!

  • avatar

    that it real and Toyota know about it ! when I bought my prius the dealer suggested me “don’t use cruise control until 3000 miles” because “it might working strange” … (something like that)

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