1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Strange Braking Behavior

Discussion in 'Gen 2 Prius Main Forum' started by ibis315, Aug 6, 2007.

  1. ibis315

    ibis315 New Member

    Joined:
    Mar 31, 2004
    13
    0
    0
    Location:
    San Jose, CA
    Has anyone felt the Prius accelerate while braking, especially when it hits a dip? I've felt this more than once. Moderate braking and one front wheel hit a small dip in the road. The Prius ICE speeds up and the car seems to accelerate instead of slowing down. Anyone else?
     
    #1 ibis315, Aug 6, 2007
  2. Sufferin' Prius Envy

    Sufferin' Prius Envy Platinum Member

    Joined:
    Jul 7, 2004
    3,998
    17
    0
    Location:
    USA
    Vehicle:
    Other Non-Hybrid
    <div class='quotetop'>QUOTE(ibis315 @ Aug 6 2007, 11:28 AM) [snapback]491389[/snapback]</div>
    1) Your Prius is not accelerating under the condition you are describing. It is, however, not decelerating at the same rate for that fraction of a second when the braking system is sensing that bump or dip in the road as a condition in which it needs to correct with the ABS system.

    Yes, this has been described many times by many people here on PriusChat. It's not dangerous . . . unless your ICE is actually speeding up . . . which I doubt.

    2) What makes you say the "The Prius ICE speeds up"????
    It is a very quiet ICE under normal loads and there is no tach. Is this a seat of the pants "feeling" . . . or do you have a Scangage hooked-up to the car?

    Don't worry about it. Continue to brake normally. It is one of the funny little idiosyncrasies of the Prius.
     
    #2 Sufferin' Prius Envy, Aug 6, 2007
  3. efusco

    efusco Moderator Emeritus
    Staff Member

    Joined:
    Nov 26, 2003
    19,891
    1,191
    9
    Location:
    Nixa, MO
    Vehicle:
    2004 Prius
    Model:
    N/A
    It doesn't accelerate, but the degree of deceleration decreases...giving the sensation of that affect.

    When braking moderately, if you hit a bump/pot-hole the regen braking will disengage, to get the exact same amount of friction braking the brake pedal needs to be depressed a little more.

    You're not gaining speed, you're just not losing speed as quickly as you were before the bump.
     
    #3 efusco, Aug 6, 2007
  4. Danny Hamilton

    Danny Hamilton Active Member

    Joined:
    Apr 30, 2007
    926
    94
    0
    Location:
    Greater Chicagoland Area
    Vehicle:
    2007 Prius
    Model:
    N/A
    <div class='quotetop'>QUOTE(ibis315 @ Aug 6 2007, 01:28 PM) [snapback]491389[/snapback]</div>
    Nah, I haven't felt it accelerate while braking.

    I have felt it decelerate less quickly (if you aren't paying close enough attention, this can feel like acceleration) when anti-lock brakes kick in.
     
    #4 Danny Hamilton, Aug 6, 2007
  5. slair

    slair Ubër Senior Member

    Joined:
    May 11, 2007
    404
    0
    0
    Location:
    Lafayette, IN
    Vehicle:
    2005 Prius
    Gas on the right, brake on the left. Just remember that....

    Just kidding, but couldn't resist. :p
     
    #5 slair, Aug 6, 2007
  6. chogan

    chogan New Member

    Joined:
    Mar 31, 2006
    590
    0
    0
    Location:
    Vienna, VA
    <div class='quotetop'>QUOTE(ibis315 @ Aug 6 2007, 02:28 PM) [snapback]491389[/snapback]</div>
    Same response as those above -- ABS is sensitive, cuts out the braking momentarily when you hit a bump in the road. I find it particularly true when headed downhill, and I've had the same thing happen when (e.g.) pulling onto the gravel shoulder of a road. Definitely scared me the first few times that happened, but 1) I've learned to avoid setting it off and 2) only rarely does it trigger unexpectedly and I now know what it is. I'd never had a car do this before I got a Prius. The good news is that you can both adjust your driving to avoid it and get used to it when it happens. It no longer bothers me (but I remain very cautious when pulling off the road.)
     
    #6 chogan, Aug 6, 2007
  7. Sufferin' Prius Envy

    Sufferin' Prius Envy Platinum Member

    Joined:
    Jul 7, 2004
    3,998
    17
    0
    Location:
    USA
    Vehicle:
    Other Non-Hybrid
    <div class='quotetop'>QUOTE(efusco @ Aug 6 2007, 11:42 AM) [snapback]491400[/snapback]</div>
    Do Oh, I think you may be correct. If the friction brakes aren't engaged, it wouldn't be the ABS system causing this sensation . . . unless the ABS also cuts-out the regen braking. :huh: Something way below my level of Priiknowledge to discern.
     
    #7 Sufferin' Prius Envy, Aug 6, 2007
(You must log in or sign up to post here.)