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Investigation Reveals Prius Brake Problems May Preceed 2010 Model-Year

Will earlier models require recall or service actions, as well?

by on Feb.08, 2010

(c)  2009

(The following story has been revised due to breaking news of the Toyota Prius recall. Click Here for that story)

Most observers anticipate a recall of the 2010 Toyota Prius to solve brake problems, but could earlier models face similar action?

How far back do potential braking problems with the Toyota Prius – the world’s most popular hybrid and the best-selling car of all types in Japan – go?  Research by suggests the answer is much further than initially believed, and could involve vehicles dating back to the 2005 model-year or even earlier.

After initially downplaying complaints by owners that 2010 Prius brakes could release unexpectedly, the troubled Japanese manufacturer’s CEO Akio Toyoda admitted the maker must “face up to facts,”  and recall 430,000 vehicles, including not only its best-selling hybrid but also the Lexus HS250h, a luxury model using essentially the same technology.

But even as Toyota prepares for another embarrassing recall, an investigation by finds that complaints about the hybrid’s brakes and other traction systems may extend back well before the launch of the third-generation Prius, last spring.  This magazine’s reporting team went into the extensive National Highway Traffic Safety Administration files for the Prius and found hundreds of customer complaints either directly detailing problems with Prius brakes prior to the 2010 model-year, or outlining compound issues that appear to involve both brakes and accelerator issues.

And that’s on top of a series of other problems, such as sudden headlight failures and unexpected powertrain shutdowns, that have been identified with the vehicle, which has become a favorite for both environmentally-minded and high-tech-oriented buyers in the U.S. and abroad. (Click Here for more on that story.)

"Braking" News!

Observers suggest a consistency to the reported Prius issues, in that most seem directly linked to the vehicle’s numerous electronics systems – a fact one of the nation’s best-known “geeks,” Apple co-founder Steve “Woz” Wozniak, pointed out earlier in the week when he told various news media his car would “go wild,” at times due to an apparent glitch with its cruise control system.  And while both safety experts and Toyota officials alike have registered frustration at trying to reproduce such problems, Wozniak said he could make his Prius act up at will. first reported problems with the 2010 Prius brakes on December 24, 2009.  Owners like New York City’s Robert Becker have complained repeatedly – both the Toyota and to the National Highway Traffic Safety Administration – that the brakes have an unsettling tendency to release for up to a second when the vehicle hits a pothole, bump or icy patch.

Toyota now blames the “aggressive” programming of the 2010 Prius’s anti-lock brake system, or ABS, which is designed to prevent skids by pumping the brakes.  The situation appears to be compounded by the dual-function brakes on the hybrid, which are designed to initially regenerate energy normally lost in braking and store it in the vehicle’s batteries.  Under more aggressive braking, or if the vehicle senses a skid, conventional hydraulic brakes take over.

The Prius/HS250h recall comes nearly a week after Toyota reversed course, initially denying the hybrids had braking problems and then, last week, saying it had already implemented a “fix,” in January, for vehicles rolling down its assembly lines.  A spokesman, Mike Michels, explained that the company had to confirm the repair, involving reprogramming software in the Prius brake controller, could be properly duplicated with vehicle already “in the field.”

The bigger question, some observers now ask is whether Toyota is looking at problems that could extend back prior to the 2010 model-year, something that a number of owners have been reporting to Toyota, the NHTSA – and to, which has been hearing about brake-related issues dating back to as early as the 2005 model-year.

Among those are Jeff Zuhlke, of Wales, Wisconsin, who says he has experienced the feeling of brake loss, “many times,” under a number of conditions that would not be likely to disrupt the operation of other vehicles, “such as when I’ve gone over small depressions in the road while braking. I’ve also had that same sensation whenever I come to a stop at a specific stop light that has railroad tracks near the light.”

Another motorist who has reported problems is Susan Yonish, of Cornelius, North Carolina, a retiree who claims her vehicle “had an actual crash due to the brakes not stopping the car in bumper-to-bumper traffic.”

If, as Toyota noted, last week, the Prius’s brakes could release for as much as a second, that would be the equivalent of driving 44 feet, or roughly three car lengths, at just 30 miles an hour, a significant distance in heavy traffic.

“There seems to be braking issues going back” before the 2010 model-year, claims Sean Kane, a well-known, if controversial, figure in safety-related litigation circles.  He has been an outspoken critic of Toyota in regards to reports of so-called “unintended acceleration,” issues the maker is hoping to address through a pair of recent recalls, one to prevent carpet entrapment and the other to deal with sticky accelerators.

But like a number of critics, Kane, head of Safety Research and Strategies, Inc., in Rehoboth, Massachusetts, has questioned whether there are electronic gremlins at work, as well, particularly with the Prius, where reports of brake problems and of unintended acceleration, which he says, “may be related.”

Electronic glitches do seem to be showing up in the Prius, and in more than just the latest model, based on federal documents covering a range of issues, such as intermittent headlight failures.  How serious these problems are, and how they differ from other automakers’ electronic issues, remains to be seen. In the current atmosphere, many self-interested parties are piling on to a wounded Toyota, whose credibility has been severely damaged, and is now in the impossible position of trying to disprove a negative.

Toyota officials insist that the braking problem – which they initially downplayed – is limited to the 2010 model-year.  But it’s unclear why that would provide a sharp delineation.  Though the new model is billed as the third-generation hybrid, and has undergone some distinctive exterior and interior body updates, Toyota officials made a point of saying that there were no significant changes to the vehicle’s distinctive Hybrid Synergy Drive system, even though the displacement of the engine was bumped up to 1.8 liters.

Spokesman Michels says the key difference is not the drivetrain, but a recalibration to “reduce ABS over-sensitivity.”  Nonetheless, Toyota has previously acknowledged that there were some issues with earlier Prius traction control technology, which also involved the programming of the hybrid’s brake controller. (ABS, traction control, electronic stability control and various other technologies all rely, at least in part, on braking to improve the stopping, handling and stability of today’s cars, including Prius.)

And Toyota’s credibility has been stretched thin by recent events, including the ongoing pair of recalls, affecting more than 8 million vehicles, for unintended acceleration.  When the first recall was announced, last October, the automaker pointed its corporate finger at loose floor mats and decried talk of other possible problems as “unwarranted speculation.”  But on January 21, 2010, Toyota added millions of vehicles troubled by potentially sticky accelerators, covered under a second recall.  And while it continues to rule out electronic glitches, federal regulators are now making that possibility a high priority of their ramped-up investigation.

How far back problems with the Prius brakes do indeed go may not become clear until federal regulators and the automaker work through their extensive lists of owner complaints.  And the onging publicity involving the hybrid – the best-selling gas-electric model in the world and the single best-selling vehicle of any type in Japan – is generating a flood of new customer grievances.

But based on’s research – which was triggered by owner concerns raised before the latest headlines – it appears there is a strong possibility that braking issues date back to at least the second-generation Prius, if not before.’s Editor-in-Chief Ken Zino and Contributing Editor Joe Szczesny contributed to this report.

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24 Responses to “Investigation Reveals Prius Brake Problems May Preceed 2010 Model-Year”

  1. Carol King says:

    Thank you so much for this story — a real public service. I haven’t had any issues with my 2007 Prius but I am watching for news of a recall. NHTSA should have been much more aggressive with Toyota. Apologies from corporate officers don’t count for much when lives have been lost because of their reluctance to take responsibility.

  2. George Kasica says:

    So now that Toyota is going to recall the 2010 models how long or what are they going to do with the others like the 2006 I’m driving that has exhibited a similar issue? Latest info seems to be they MAY issue a TSB for them but that is not even assured as this time.

    It still feels like Toyota has to be dragged to fix this kicking and screaming “there’s no real problem”

  3. Patrish C says:

    My 2005 Prius has always had this brake problem…always on bumpy roads or a slick spot, I lose braking power for an instant. Pretty disconcerting each time it happens.

    • tdb says:

      Hi, Patrish,
      Please contact me directly using the site’s e-mail server. I would very much like to discuss your experiences.
      Paul A. Eisenstein

  4. Chris says:

    This braking situation was recreated on TV by a Chicago ABC affiliate:

    Video shown here:

    Full braking functionality is actually fully available, if you feel the brakes loosening due to a pot hole, all you have to do is depress the brakes a little further. Also, this braking phenomena only happens in light-braking and not in hard braking.

    • tdb says:

      Thank you for the update and link. It does appear that recovering braking is not especially difficult, under most circumstances but that’s almost missing the point(s): 1) There should be no reason that a driver need to alter their actions to get brakes to work properly. We are long past that stage and, if anything, ABS was designed, in part, to avoid our having to learn to do such things as pump the brakes; 2) One cannot assume that even a good driver will always do the correct thing if something with the vehicle fails to operate correctly. In other words, even a momentary lapse in brake function can trigger a mistaken response and 3) Even if a driver does do the right thing, Toyota has suggested that braking can be lost for up to 1 second. That may not sound like much but even at the relatively slow speed of 30 mph, you’ll travel a full 44 feet, or nearly three car lengths, in that time. At 70, the highway speed in Michigan, you’ve gone more than 100 feet, enough to cause a reasonably serious accident.
      Nonetheless, until Toyota corrects the problem with the 2010 Prius, it is good for owners to know what to do if the brakes do cut out.
      Paul A. Eisenstein

  5. Watt D Fark says:

    OH what a feeling…when you think your brakes don’t work!

  6. linda says:

    I just complained to the Toyota dealer last weekend about the braking issue on my 2008 Prius and they claimed nothing was wrong.

    At first they tried to blame it on ice and snow and I had to correct them that I meant rough or uneven pavement, even just a bump in the road.
    This was not a weather related complaint.

    I also complained of a bad glare of fluorescent green light across the windshield at night coming from the speedometer that impairs my line of sight. Their response was they could not duplicate the problem and I needed to come back.

    Toyota is failing in my book.

  7. Anonymous says:

    The problem with ABS brakes spontaneously releasing while your foot is on the brake pedal goes back a long ways… I had this problem of the brakes releasing for a fraction of second while stopped at traffic lights with my brand new 1989 Chevy Blazer. (This was the first year for ABS brakes for this model vehicle.)
    GM and the dealership put me through hell for about four months, but GM/the dealership ultimately repurchased the vehicle from me, although they never admitted any problem with the brakes.
    I ended up filing complaints with the NHTSa and the BBB, and sued GM in small claims court to recover my rental car costs. I lost this claim, but got so pissed off with the unfairness of the whole situation that I went to law school and became a lawyer.

  8. CPAUL says:

    my wife had a braking problem in a 2009 prius, and icy road and the brakes did not work, resulting in a crash with the car in front of her.
    The repair was very expensive. I’m wondering what can we do ??

  9. alan y says:

    Your story is the most accurate and thoughtful of any article
    I have read on the subject of Prius braking issues.
    I own a 2005 Prius and as many owners of later model
    Priuses will attest, I have experienced the slippage or pause
    in braking over rough surfaces over the past 5 years.
    For any open minded reader, or for Toyota or the US Govt,
    to conclude that the braking issue is limited to 2010 Prius
    models is inconceivable. It is a widespread issue and it is
    dangerous. I will never trust Toyota and will never buy another
    Toyota vehicle is they, despite overwhelming evidence over the years, fail to correct the problem for all vehicles with similar
    braking systems and software.

  10. Peter Pelosi says:

    I have a 2009 Prius and have experienced the braking problem. It happens when I’m slowing down or when I hit a bump as I brake, I sense a feeling of the car moving forward. I also noticed my skidding light goes on. This appears to be not only a 2010 Prius problem.

  11. [...] First and second generation Prius are not affected by this recall (but you may want to read this article about that). [...]

  12. [...] First and second generation Prius are not affected by this recall (but you may want to read this article about that). [...]