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How To Statically Bleed Off Brake Assist To Feel Hydraulics Only

Discussion in 'Gen 3 Prius Technical Discussion' started by Susan4ET, Mar 3, 2010.

  1. Susan4ET

    Susan4ET Member

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    In order to statically test the feel of brake application if the power assist failed for any reason is there any way to easily deactivate the electric pump that keeps this pressure built up even when the car is 'off'? Would doing this 'test' create other system/ECU problems that would be difficult to address/resolve?

    If you were parking your Prius on a hill and power assist failed or the assist pressure was depleted what would the brake pedal force feel like? Could the force required be great enough that a driver not aware of the failure might describe the brake pedal as locked up--that he/she couldn't push down on the brake at all--no movement? Thanks.
     
    #1 Susan4ET, Mar 3, 2010
  2. qbee42

    qbee42 My other car is a boat

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    First, let me make a minor correction. On a couple of posts you have referred to the power brakes as "brake assist". While this term is correct in the general sense, Toyota uses it as the name of a brake feature. On the Prius, Brake Assist senses that the driver is doing a panic stop, and applies full braking power in advance of the brake pedal being fully depressed. This has the effect of reducing reaction time.

    Getting back to power brakes, on the Prius, when the power assist is working, the brake pedal presses against a "stroke simulator", which makes it feel like you have a normal hydraulic power braking system. When the power assists fails, the stroke simulator is disconnected and the master cylinder directly drives the hydraulic brakes. The difference in feel is the same as it is with most any car. The brakes still work, but you have to push harder. I suppose someone could misinterpret this as a stuck brake pedal, but it doesn't seem likely.

    If you really want to see what it feels like, pull the fuse to the brake system. You will have to active the brakes a few times to use up the accumulated pressure and to drain the super-capacitor backup power. Pulling the fuse will log a code.

    Tom
     
    #2 qbee42, Mar 3, 2010
  3. Susan4ET

    Susan4ET Member

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    Sorry about the terminology mix up. "Power assist" it is. I remember reading about the real "brake assist" too, but wasn't certain and didn't want to read the manual section again.

    I know about what it really feels like from other cars. I was curious if there was a way to shut off the brake assist but I don't want to log any codes.
     
    #3 Susan4ET, Mar 3, 2010
  4. David Beale

    David Beale Senior Member

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    Suzan, you need to get yourself a Scangauge II if you want to continue messing around with the car. You can then reset any codes you happen to trigger.

    If you are just sitting still, you won't notice any difference with or without power assist braking. The opposite is true of power steering. If you are moving above about 15 MPH you won't notice if the power steering is off. If you are sitting still you will notice it.

    Either way, the Prius is a light car, only about 3000 lbs +or- 200. You will find braking and steering work just fine with or without power assist.
     
    #4 David Beale, Mar 4, 2010
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