My car decelerates very quickly as soon as I take My foot of the gas

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Lauren Vandergrift, Mar 5, 2020.

  1. Lauren Vandergrift

    Lauren Vandergrift New Member

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    My car started decelerating quickly as soon as I take My foot off the gas. The emergency brake was not engaged. And it happened twice today, so I know I didn't put it in B both times. Anyone have any suggestions??
     
  2. ChapmanF

    ChapmanF Senior Member

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    If there's a lightly-traveled road near you where you think you could drive ten or fifteen minutes without having to touch the brakes, with near the end a big noncrowded parking lot that you can turn in to while slowing in B and stop without the brakes, then you can get out of the car and feel all four brake rotors. All four should be stone cold after a trip like that. If one is hot, that brake is dragging.

    Key to the test is to stop with no use of the brake. I usually make a big U in the parking lot at the end in B mode, so I'll be under 6 mph coming back the other side of the U, and at that speed the car will allow shifting to R, which will take the remaining speed off. Just stab the brake pedal down at the instant the car is stopped, before it's moving in reverse. That won't generate heat.

    If you have to use the brakes even a little when stopping at the end; they'll be warm from that and the test won't tell you much.

    It's good to scope out the test route first and make sure it's lightly traveled enough.
     
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  3. MickyMatter

    MickyMatter Active Member

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    I'd like to add: In N you can roll out until it stops without braking.

    SM-G950F ?
     
  4. ChapmanF

    ChapmanF Senior Member

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    If the parking lot is big enough and empty enough, or has an uphill grade you can use.

    If the brakes aren't dragging, it can roll pretty well!
     
  5. fuzzy1

    fuzzy1 Senior Member

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    When I've had brake drag problems in past cars (before Prius), I've been able to use a little bit of brakes at the end for the final stop and still get the answers I needed. The non-dragging brakes were a bit warm but not hot. The badly dragging brakes were HOT! (The worst cases were smoking, the less severe ones were not.)

    With my light braking, it won't distinguish between light drag and no drag, but it will get identify worse cases.
     
    #5 fuzzy1, Mar 5, 2020
    Last edited: Mar 5, 2020
  6. ice9

    ice9 Active Member

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    Sometimes regenerative braking can appear to be quite noticeable when the tractor battery is recharging when it gets low... ...even when you are not trying to slow down. You take your foot off the accelerator and instead of coasting, the vehicle actually slows down as if you were applying the brakes. Part of it is sensory illusion - i.e. the deceleration appears more noticeable when you are not expecting any deceleration - and part of it is real.
     
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  7. ChapmanF

    ChapmanF Senior Member

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    Definitely. All the same, we are driving highly optimized MPG machines, so being able to confirm those rotors are genuinely cold brings extra satisfaction.
     
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  8. PriusCamper

    PriusCamper Senior Member

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    Roll down all your windows and listen for noises when you take your foot off the gas... Also turn to both the left and right to see if the abnormal deceleration increases more in one of those directions.
     
  9. vvillovv

    vvillovv Senior Member

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    wrong thread oops
     
    #9 vvillovv, Jan 1, 2023
    Last edited: Jan 1, 2023
  10. pasadena_commut

    pasadena_commut Active Member

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    Coast to a stop in neutral going uphill. (Remember that the shift has to be held at N for a couple of seconds before the transmission will shift to that.) Once the car drops to 0 mph stepping on the brake, applying the parking brake, and putting it in Park will not heat up the wheels.
     
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