Crashed 04 WRX - ABS Failure?
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This is a discussion on Crashed 04 WRX - ABS Failure? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I got my 04 WRX 6 weeks ago. For the 5 weeks I drove it, the ABS would engage regularly ...

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    Registered User kempobmx1's Avatar
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    Crashed 04 WRX - ABS Failure?

    I got my 04 WRX 6 weeks ago. For the 5 weeks I drove it, the ABS would engage regularly under heavy braking on uneven surfaces (as I would expect). Then a week ago I entered a turn at a speed well beyond what I should have, and crashed due to severe understeer. After the crash I realized my ABS never engaged. Do you have to bring your wheels to full lock for the ABS to engage? I thought the system just had to sense that the vehicle speed and wheel speed no longer matched perfectly. During the turn I got on the brakes hard to try to reduce understeer but I did not stand on them, so as to try to avoid full lock and/or oversteer. Was that what caused the ABS to not engage or might they have failed? If they should have engaged under the above conditions that may help me write off the crash as no-fault with the insurance company.

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    Moderator Donkey's Avatar
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    Quote Originally Posted by kempobmx1 View Post
    I got my 04 WRX 6 weeks ago. For the 5 weeks I drove it, the ABS would engage regularly under heavy braking on uneven surfaces (as I would expect). Then a week ago I entered a turn at a speed well beyond what I should have, and crashed due to severe understeer. After the crash I realized my ABS never engaged. Do you have to bring your wheels to full lock for the ABS to engage? I thought the system just had to sense that the vehicle speed and wheel speed no longer matched perfectly. During the turn I got on the brakes hard to try to reduce understeer but I did not stand on them, so as to try to avoid full lock and/or oversteer. Was that what caused the ABS to not engage or might they have failed? If they should have engaged under the above conditions that may help me write off the crash as no-fault with the insurance company.
    0 The 5.3i type ABS used in the lmpreza has a hydraulic control unit, an ABS control module, a
    valve relay and a motor relay integrated into a single unit (called “ABSCM & H/U”) for circuit simplicity
    and reduced weight.
    0 The ABS electrically controls the brake fluid pressure to each wheel to prevent the wheel from
    locking during braking on slippery road surfaces, thereby enabling the driver to maintain the
    directional control.
    0 If the ABS becomes inoperative, a fail-safe system is activated to ensure same level of braking
    performance as with a conventional brake system. In that case, the warning light comes on to indicate
    that the ABS is malfunctioning.

    0 The ABS is a 4-sensor, 4-channel system; the front wheel system is an independent control design*’,
    while the rear wheel system is a select-low control design*2.
    *I : A system which controls the front wheel brakes individually.
    *2: A system which applies the same fluid pressure to both the rear wheels if either wheel starts
    to lock. The pressure is determined based on the lower of the frictional coefficients of both wheels.

    C: PRINCIPLE OF ABS CONTROL
    When the brake pedal is depressed during driving, the wheel speed decreases and the vehicle
    speed does as well. The decrease in the vehicle speed, however, is not always proportional to the
    decrease in the wheel speed. The non-correspondence between the wheel speed and vehicle
    speed is called “slip” and the magnitude of the slip is expressed by the “slip ratio” which is defined
    as follows:
    Slip ratio = Vehicle speed - Wheel speedNehicle speed x 100%
    When the slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed; when it is
    loo%, the wheels are completely locking (rotating at a zero speed) while the vehicle is moving.
    The braking effectiveness is represented by the “coefficient of friction” between the tire and road
    surface. The larger the Coefficient, the higher the braking effectiveness. The diagram below shows
    the relationship between the coefficient of friction and the slip ratio for two different road surface
    conditions (asphalt-paved road and icy road), assuming that the same tires are used for both the
    conditions and the vehicles are moving forward. Although the braking effectiveness (coefficient
    of friction) depends on the road surface condition as shown and also on the type of the tire, its peak
    range generally corresponds to the 8 - 30% range of the slip ratio.
    The ABS controls the fluid pressure to each wheel so that a coefficient of friction corresponding
    to this dip ratio range is maintained.

    In short you crashed because you driving failed,not ABS
    Resident Adviser @ WTF Tuning, LLC
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    1998 FORESTER S




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    Good news, everyone! xxxxxxxAnub1s's Avatar
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    Highly doubt it. Sounds like you're just too used to driving like a jackass and crashed as a result.

    Sorry to be an ass here, but you crashed because of idiocy, yes it was a possibility that something failed, but when you're turning and sliding, braking is the last thing that's going to help you.
    Cody
    Hawk-Eye Alliance #727 N.E.R.D #255.255.255.0

    Your nighttime volunteer of near-useless information.
    Good news, everyone!

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    Registered User kempobmx1's Avatar
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    To the first response, thanks for the info but I knew that last bit.

    To the second response, keep the useless comments coming. I admitted in my original post that I took a turn I had no business taking. I don't need a lesson in my degree of stupidity causing a car crash. I'm simply asking if the ABS SHOULD HAVE engaged for insurance purposes. The first response marginally helped with that, though I already understood the concept of how ABS works and the concepts behind slip.

    I'm just looking for whether or not my ABS was supposed to engage. I don't need a reminder that I should tone down the driving. My destroyed suspension and axle told me that just fine.

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    Moderator Donkey's Avatar
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    Quote Originally Posted by kempobmx1 View Post
    To the first response, thanks for the info but I knew that last bit.

    To the second response, keep the useless comments coming. I admitted in my original post that I took a turn I had no business taking. I don't need a lesson in my degree of stupidity causing a car crash. I'm simply asking if the ABS SHOULD HAVE engaged for insurance purposes. The first response marginally helped with that, though I already understood the concept of how ABS works and the concepts behind slip.

    I'm just looking for whether or not my ABS was supposed to engage. I don't need a reminder that I should tone down the driving. My destroyed suspension and axle told me that just fine.
    No offense but if you knew all about the information above you wouldn't need to be asking here if your ABS should have engaged or not. You should have been able to deduce this yourself. I mean how are we supposed to know with out vehicle speed, g-force,wheel speed and all the other info ABS uses to calculate how to react. You would need all that info to answer that question plus the factory set thresholds.
    Resident Adviser @ WTF Tuning, LLC
    2002 FORESTER S
    1998 FORESTER S




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    He simply abides. SD_GR's Avatar
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    I agree with Donkey. Also, it could be that you're assuming ABS is equivalent to what you are essentially describing as stability control, when in fact it is not -- stability control systems tend to use the ABS and throttle to achieve what you described as the result you expected, but ABS on its own engages when the wheels are locking up under hard braking. If the wheels are not on the threshold of locking, the ABS should stay out of things.
    WRX Info Links, Courtesy TheJ
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    Registered User 4cyturbowrx's Avatar
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    Personally the abs is a little sensative.... On a side note your driving to fast. Man up.......

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    Registered User Pactin's Avatar
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    If you were on the "edge" of your grip threshold, not even the brakes will help you. Brakes still rely on the tires.

    That said, understeer is understeer- you entered too fast.
    --Justin

    Hawk-Eye Alliance #128

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    Registered User kempobmx1's Avatar
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    Pactin, thanks. I knew that but hadn't really considered it. You're completely right. ABS would have done nothing for me regardless.

    SD_GR, I wish my car had VDC (stability control), however I'm aware that it doesn't. Under the circumstances it probably would not have helped though. I'm not denying that I made a dumb move.
    Last edited by kempobmx1; 11-22-2009 at 01:40 PM.

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