Toyota gas pedal problems

Discussion in 'General Motoring' started by MoPar Man, Feb 2, 2010.

  1. MoPar Man

    MoPar Man Guest

    As I understand it, the accelerator pedal in these toyotas are not
    connected to the engine via mechanical linkages - but instead the pedal
    position is sensed by a sensor and communicated to the engine control
    computer which actuates a servo motor to control engine RPM.

    If this is correct, then the problem is either:

    a) the pedal sensor becomes faulty and reports incorrect pedal position
    (ie - sensor reports that the driver is calling for high engine RPM)

    b) the pedal return spring mechanism does not work properly, so the
    pedal gets stuck in the accelerate position (and the sensor
    accurately reports this pedal position to the computer)

    I know that floor mats have been implicated as potentially causing (b),
    in which case it could still be argued that the pedal return spring is
    not sufficiently strong to overcome floor-mat interference.

    What I find incredible is that when either (a) or (b) happens, that the
    computer does not also recognize that the driver is also pressing the
    brake pedal and make a decision to over-ride the call for high engine
    RPM and thus drop the engine to idle RPM. This behavior should be
    mandated by the DOT / NHTSA for "drive-by-wire" accelerator-pedal
    systems. When presented with conflicting information, the computer
    should err on the side of safety.

    If the above control pattern was implimented, then if the brake-switch
    is faulty then the driver can't accelerate the car, but he can still
    control it and bring it to a safe stop.

    If drive-by-wire systems are going to be deployed like this in passenger
    cars (presumably because they require less mechanical engineering effort
    to design, construct and install) then there has to be a recognition
    that electric sensors, connections and wires can fail in ways that
    mechanical solutions can't or don't, and hence a tradeoff has to be made
    that can result in inconvienence to the owner if the control computer
    takes corrective (but safe) action based incorrect inputs.

    As a result of this Toyota debacle, I will make extreme efforts to
    insure that my next car will not have this drive-by-wire accelerator
    pedal mechanism.

    Does anyone know which car brands (other than Toyota) have this design?
    MoPar Man, Feb 2, 2010
  2. In other words, why didn't they implement the system to fail safely.

    I agree 100%.

    You know, there's a reason that air brakes work the way they do--with
    the air pressure holding the brakes OFF, such that if the air pressure
    fails, the brakes are ON.

    Fail safe. It's a good idea.
    Elmo P. Shagnasty, Feb 2, 2010
  3. MoPar Man

    Tegger Guest

    I'm not sure there are many new cars that use throttle cables anymore.

    Electronic Stability Control (ESC) and Traction Control (TRAC)
    effectively require that the PCM have full control over throttle
    openings. A mechanical cable makes ESC and TRAC harder to implement.

    ESC seems to be universal now:

    If the sensor is faulty, the system's fail-safe defaults to idle.

    There is no problem with the sensors themselves.

    That's what's happening. The new metal-bar fix prevents the stickiness.

    That's hard to square with reality.

    That a look at the picture on Transport Canad'a website regarding this

    No spring would lift /that/ pedal, I think.

    Toyota is changing the PCM programming to kill power if the brake and
    gas are pressed at the same time.

    My thinking? People with winter boots or with big feet will accidentally
    hit gas and brake at the same time in traffic and end up getting
    rear-ended. I'm not sure Toyota can win this one no matter how hard
    they try.
    Tegger, Feb 2, 2010
  4. MoPar Man

    C. E. White Guest

    The claim is that there is a binding in the mechanism that prevents the
    return spring from returning the pedal in the desire manner. I've seen an
    illustration of the piece that they are adding to correct this issue, but I
    can't understand how it will fix the problem. I am hoping to get a good look
    at a "repaired" unit.
    It is my understanding that Toyota is going to implement this sort of fail
    safe system at least on some cars.

    C. E. White, Feb 2, 2010
  5. MoPar Man

    Rob Guest

    Feds look at Toyota electronics as source of acceleration defects

    February 2, 2010 - 4:21 pm ET

    WASHINGTON -- The U.S. Department of Transportation is looking into whether
    Toyota Motor Corp.'s problems with unintended acceleration can be traced to
    defects in the electrical controls rather than just the mechanical problems
    cited by the automaker, a Transportation official said today.

    "We're not finished with Toyota and are continuing to review possible
    defects and monitor the implementation of the recalls," Transportation
    Secretary Ray LaHood said in a statement.

    When asked whether the federal review includes possible electrical problems
    with Toyota vehicles, a Transportation official who asked not to be
    identified responded in an e-mail, "Yes."

    Toyota spokesman Jim Wiseman could not be immediately reached for comment
    this afternoon about the expanded federal review.

    Since announcing its recalls and a production halt last week, Toyota has
    maintained that problems with unintended acceleration were limited to floor
    mat interference and sticky accelerator pedals.

    Shinichi Sasaki, Toyota's vice president in charge of quality, today denied
    accusations that electronic malfunctions were contributing to the reports of
    unintended acceleration.

    "We have not come across any case in which we have found a malfunction,"
    Sasaki said in an interview in Japan. "But if any additional reports arise,
    we will conduct testing using all technology at our disposal."

    Also, in a full-page advertisement that ran in many U.S. newspapers today,
    Toyota Motor Sales U.S.A. President Jim Lentz said: "We have launched a
    comprehensive plan to permanently fix the vehicles we've recalled because in
    rare instances, accelerator pedals can, over time, become slow to release or
    get stuck. We know what's causing this and what we have to do to fix it."

    But Safety Research & Strategies, a consulting firm, said in a posting on
    its Web site: "Neither floor mats nor sticking accelerator pedals explain
    many, many incidents" of unintended acceleration.

    Read more:
    Rob, Feb 2, 2010
  6. MoPar Man

    Bill Putney Guest

    FWIW, one thing that aggravates stuck accelerator type problems in any
    vehicle that powers the brake booster with engine vacuum (98+% of all
    passenger vehicles) is that when the throttle is open much above the
    idle position, the engine vacuum to the booster is almost nil, so once
    the initial booster charge is depleted (typically happens with the 2nd
    or 3rd stab of the brake pedal), the brakes are almost useless against
    the pull of the engine.

    You can see this for yourself in your own vehicle - with no other
    traffic around and at cruising speed, simultaneously push on the brakes
    and the accelerator - while still pushing the accelerator (you don't
    have to push the accelerator very much to see this effect), release the
    brakles and apply them again. You will be amazed at how ineffective the
    brakes are. Again - it is not due to the engine being that more
    powerful than the brakes normally are - it is due to the vacuum not
    being available to re-charge the booster once the initial couple of
    stabs at the brakes has occured.
    Bill Putney, Feb 2, 2010
  7. MoPar Man

    Rob Guest

    Rob, Feb 2, 2010
  8. MoPar Man

    MoPar Man Guest

    Yes, this is true. I had a manifold vacuum gauge on my '65 Dodge and
    could watch the vacuum change depending on my speed and gas-pedal

    I thought there was some sort of design rule (if not gov't regulation)
    that a car's brakes must be able to hold a car in-place regardless how
    powerful the engine was. Presumably this test would be performed from a
    stand-still. In these cases of run-away Toyota cars, it's
    understandable that given a car that's already going 30 - 60 mph with an
    engine running wide-open, that the brakes simply can't overpower the
    inertia the car already has plus the power being delivered by the engine
    (and combined with almost no vacuum boost assist).

    A USA-today article from last week mentioned the mindset behind this
    faulty computer-control situation is that the computer is programmed to
    not judge what the driver's intentions are if it seems that both the gas
    pedal and brakes are being applied at the same time. I think that's a
    coward's way of explaining it.

    One possible (but un-voiced) explanation is that someone has the patent
    on having the computer reject the throttle-position sensor when the
    brake is depressed (and it would cost a fortune to license it). Another
    explanation is that it might result in a *lower* level of liability
    against Toyota if it simply kept building cars with the same faulty
    control pattern programmed into the computer instead of introducing a
    fix for newer cars while leaving existing cars alone.

    Today on the web I read an article showing in good detail exactly where
    these pedals are sticking. It looks like 5 small teeth mesh with each
    other (3 on the stationary fire-wall side, 2 on the moving pedal) and if
    the pedal is pressed hard enough, these teeth end up sticking together.
    The proposed fix is a metal bar that acts like a stop to prevent these
    teeth from meshing to the point where they bind up. There appears to
    already be a stop that's built into the mechanism, but it's smaller (and
    shorter) than the proposed fix.

    (I have no idea what the teeth are for - perhaps they are part of the
    actual position sensor? Sensing electrical resistance as a function of
    meshed area? Or perhaps optical?)

    The article went on to explain that many German cars have the correct
    computer programming (ie - brake over-rides the throttle sensor). Some
    hi-end Jap cars might also have this. My theory is that if the car is
    expensive enough to indicate that the owner has enough $$$ to sue in
    case of injury, then the auto maker programs the brake over-ride
    function into the computer.

    There is one possible reason have the throttle pressed down while riding
    the brakes - that's if you're stopped in traffic on a hill (facing up)
    and you don't want to drift down and hit the guy behind you when you
    take your foot off the brake. In that case, if you take one more sensor
    measurement (vehicle speed as measured by the transmission output speed
    sensor) then you can develop a set of rules as to when to over-ride the
    throttle sensor and when not too.
    MoPar Man, Feb 3, 2010
  9. MoPar Man

    MoPar Man Guest

    In that situation, presumably you're starting from a stopped position,
    you get a green light and you take your foot off the brake and shift it
    to the gas pedal, where you come down but end up hitting both pedals.
    Your brake lights blink for a split-second, but they'll still be red,
    you won't advance very far (because your pressing on both pedals) and
    the guy behind you won't get the impression that you're moving to the
    extent that he's going to start moving and run into you.
    MoPar Man, Feb 3, 2010
  10. MoPar Man

    QX Guest

    My 2005 Subaru Forester had drive by wire. Never had a problem with
    it, nor do I know of any similar problems in other Subie models.
    QX, Feb 3, 2010
  11. MoPar Man

    Wesley Guest

    Our 2002 Isuzu Trooper has this sort of system. I'm guessing it was
    relatively new at the time as I recall seeing it mentioned as being a
    "feature" or whatever. I've never heard any reports of problems with the
    system... I'm guessing it was used in all the 98-02 models.

    Interestingly enough, there was a recall on our 94 Trooper a few years back
    for an issue with the throttle sticking - and it's a "traditional" throttle.

    I think a lot of the new cars are indeed going with a "drive by wire"
    system. I'm nearly positive that is how it works on the 05 Grand Marquis we
    have as a company car at work...

    Wesley, Feb 13, 2010
  12. MoPar Man

    Clive Guest

    Drive by wire has to be just about standard here in the EU as emissions
    are tightening every five years or so and ordinary injection whether
    mechanical or electrical can't cope, so everything has to be controlled
    by a pre-mapped microchip. It's not more unreliable than a straight
    forward cable, remember the Ford Explorers with the sticking throttles,
    which turned out to be a fault with the cruse control cable holding both
    venturi of the carburettor fully open against the drivers wishes. (See
    Clive, Feb 13, 2010
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