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Small surges when decelerating

Discussion in 'Gen 2 Prius Technical Discussion' started by Fibb222, Aug 10, 2008.

  1. Fibb222

    Fibb222 New Member

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    Lately, my 2004 prius seems to be acting somewhat differently - when I decelerate (lightly braking) from say 40 mph to 20 mph, it sometimes gently surges/thumps a wee bit. i.e. the drivetrain pulses or like the braking motor hiccuped. There is no check engine light or anything. I seem to be getting normal mileage and everything else appears normal but I thought I might spend $80 at the dealer to have the car checked over. I have about 7 months/11000 kms left of drivetrain warranty on the vehicle.

    Anybody ever notice anything like this? It's hard to describe. It's a subtle thing, but I haven't noticed it before two weeks ago. I am pretty in tune with the way the car normally behaves. Thanks
     
    #1 Fibb222, Aug 10, 2008
  2. Bob64

    Bob64 Sapphire of the Blue Sky

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    Is the road bumpy?
     
    #2 Bob64, Aug 12, 2008
  3. abq sfr

    abq sfr New Member

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    Funny, I just posted a similar thread here. If you hit rough road or a pothole, it almost feels like the brakes quit braking for a second, and I think they do. Its normal, and disturbing if it happens as your are closing the distance on the car in front of you :eek: I think iit might be caused by a sudden transition from motor regen to friction brakes caused by the rough road/pothole.
     
    #3 abq sfr, Aug 12, 2008
  4. Fibb222

    Fibb222 New Member

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    Hmmm... Funny I never noticed it before after a year and a half of driving it. Also, I think it has stopped... I'll post more info if things change again.
     
    #4 Fibb222, Aug 12, 2008
  5. Cessna157

    Cessna157 Junior Member

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    It is just the anti-skid system acting normally. If you are braking and slip into a pot-hole or similiar road hazard, the tire will slip just a bit. It seems the anti-skid on the prius is very sensitive, and activates at the slightest change in tire speed. Mine does this occasionally, and sometimes the light will flash once or twice.
     
    #5 Cessna157, Aug 13, 2008
  6. richard schumacher

    richard schumacher shortbus driver

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    Grit, gravel, sand, oil, squished bugs, moguls, washboarding, or water on the road, anything that makes the tires lose their grip momentarily can cause this.
     
    #6 richard schumacher, Aug 14, 2008
  7. tripp

    tripp Which it's a 'ybrid, ain't it?

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    On my way home from work I have to decent a VERY steep hill on a dirt /gravel road. I get this a lot and it's annoying and a bit disconcerting, esp when there's snow/ice. It is probably the one thing I wish that they would have implemented better.
     
    #7 tripp, Aug 15, 2008
  8. fed123

    fed123 Member

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    I find that I can prevent this if I see a bump coming by taking my foot off the break.
     
    #8 fed123, Aug 15, 2008
  9. tripp

    tripp Which it's a 'ybrid, ain't it?

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    it's tough though when you're on a steep inline because the car will actually accelerate, even in 'B' mode. If it's snowy it's even more dodgy to do that. You really just have to creep along and try to not build up too much momentum.
     
    #9 tripp, Aug 15, 2008
  10. Fibb222

    Fibb222 New Member

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    After driving more around town today, I've determined it is not traction control or anti-skid. The engine or motor surges slightly for moment usually as I'm slowly braking/decelerating from 65 km/h to 35. It's a new thing and I don't know what is causing it but I don't think it has anything to do with traction. Puzzling...
     
    #10 Fibb222, Aug 17, 2008
  11. Sheepdog

    Sheepdog C'Mere Sheepie!

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    Tripp, Do you go to B mode when coursing down that big hill? seems it would help but may not help the braking lapse. I havent seen it yet here but I live in Florida and the hiway exit is the steepest thing I see.
     
    #11 Sheepdog, Aug 18, 2008
  12. SSimon

    SSimon Active Member

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    Fibb,

    I've had this happen to me and it's very sporadic. My happenings had nothing at all to do with terrain conditions. Seems to happen mostly when I'm in electric mode. It's a very definitive cycle pulse. It hasn't occurred in quite some time now.
     
    #12 SSimon, Aug 18, 2008
  13. hyo silver

    hyo silver Awaaaaay

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    I've noticed this, too, though it's not a new thing on my 2004. The brakes seem to stop working for a split second, even under ideal conditions. It's different than the abs or traction control, which I've also felt when the roads are slippery. Could it be the transition between electric and mechanical brakes? Wouldn't it be better for those two systems to overlap, instead of having a gap?
     
    #13 hyo silver, Aug 18, 2008
  14. Fibb222

    Fibb222 New Member

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    I think the transition between electric and the friction brakes on a gradual deceleration is supposed to happen at 8 miles/hr or something. But it does feel like that.
     
    #14 Fibb222, Aug 18, 2008
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