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Regenerative Brake won't Disengage

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by toyolover, May 14, 2014.

  1. toyolover

    toyolover Member

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    After taking off the driver's side front wheel to measure the thickness of the disc two days ago, it now makes a low whining noise similar to when the regenerative braking is engaged and charging the battery. This noise is noticeable when the car is coasting after I lifted my foot off the gas pedal. I am almost positive that the regenerative braking is being engaged too soon or stuck in engage position at all times.
    Under normal situation, I can tell when it is activated by looking at the display info center. When the car is slowing down, the regenerative brake doesn't engage right the way until I apply force (even slightly) on the brake pedal. Then I can see the charging bar moving to the left (ie. in charging battery state.)
    The situation now is that it engage the charging state before I even touch the brake pedal.
    Before I take it to the dealer, I'd like to know if there is any system reset I can do as a last resort?
    Help would be very much appreciated.
     
  2. JC91006

    JC91006 Senior Member

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    Sounds like a mg2 problem in the transaxle. How many miles on your car? When did you do your transaxle fluid change?

    SM-N900P ?
     
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  3. toyolover

    toyolover Member

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    If the transaxle fluid is the same as transmission fluid, I just had it changed by the dealer 2 weeks ago. It just passed the 100,000km mark. What is mg2?
     
  4. JC91006

    JC91006 Senior Member

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    Mg2 is the larger of the 2 electric motors in your transaxle. Did you happen to notice your problem after the fluid change?

    You could also have your brake pad stuck. Maybe you just have to lube the pins on the pads
    SM-N900P ?
     
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  5. toyolover

    toyolover Member

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    I don't think it was there until yesterday. If it was there since the fluid change, it must be very subtle until now. Is there any chance that I might have damage something just by taking the wheel off and put it back?
     
  6. JC91006

    JC91006 Senior Member

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    If you torque the wheel while it's in the air, you might have ruined the alignment, but that a big might.

    If you just removed the wheel, not sure how that can happen. Are they torqued properly?

    SM-N900P ?
     
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  7. toyolover

    toyolover Member

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    I didn't use the torque wrench (I do have one) because I don't have the correct size of socket. I hand tighten it with the Toyota wrench in the truck kit. I did tighten the nuts with the wheel off the ground but how could that ruin the alignment? Besides, I don't feel the wheel is shaking when I drive.
     
  8. JC91006

    JC91006 Senior Member

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    That tool you used requires you to push down on the wheel without anything underneath to support it. Depending on how strong you are, you could have affected the alignment. I'm just guessing, not sure if that'll cause a whining sound. In the future, always torque the wheel when is on the ground.

    The car wouldn't shake if the alignment is off.

    SM-N900P ?
     
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  9. toyolover

    toyolover Member

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    JC91006, Thanks for your input. I will get the correct socket tomorrow and re-torque the wheel nuts. Let's see what'd happen after. Will post further results again.
    (BTW: I don't think I over-tighten it by hand. I read from somewhere before that the manufacturer designed the handle of the wrench with certain length so that it becomes impossible to over-tighten it too much by hand.)
     
  10. vskid3

    vskid3 Active Member

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    Seems to me like you're being paranoid. Removing the wheel shouldn't have any affect on the regenerative braking, as that all takes place inside the transaxle by having the motor act as a generator. Prii engage regen when you let off the gas completely, that's how they're programmed. If anything, you probably just didn't notice it before.
     
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  11. fuzzy1

    fuzzy1 Senior Member

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    It sounds more like the car used to be broken, but is now fixed. A light level of regen should always start as soon as your foot leaves the gas pedal and you start coasting, before hitting the brake. The brake pedal will increase the regen, but a light level of it should already be present.

    This coasting regeneration is a 'fake engine drag', to make the car behave more similar to traditional cars and ease the transition for new drivers. When working correctly, it is less than the real engine drag of traditional cars. Many of us would like to abolish it or have the option to turn it off, but no luck yet. So we lightly touch the gas pedal to get rid of the HSI bar.
     
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  12. mtbiker53

    mtbiker53 Junior Member

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    Measure thickness of the disc?Unless you were planning on having it turned,what's the point?

    steve
     
  13. toyolover

    toyolover Member

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    To prove whether the dealer's service advisor lie or not by saying my front brake rotor and pad are up for replacement by their "visual inspection". I asked them for the remaining thickness reading of the disc and pad and they said I have to pay $150 labour charge to get it done. That's why I took off the wheels and measured it.
    The result is a surprise. The front disc is still almost 25mm which is the thickness as a new one. The front pad wear is 9mm remaining compares to a new one of 10mm. So to say the front wear is almost none after 100,000km.
    The rear disc wear is also minimal while the pad wear is 50%.
    That's amazing!
     
  14. adamace1

    adamace1 Senior Member

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    My car and all of them have regenerative braking start after you take your foot of the gas and before you push on the brake. I'm 100% sure this is normal operation.
     
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  15. toyolover

    toyolover Member

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    Took the car to the dealer yesterday. The foreman took a test drive with me and also hear the whining noise from the front wheel. After hoisting it up and banged on the driver's side front wheel, he's quite sure the wheel bearing is the problem. Fortunately, he says it is still under warranty and he is going to replace the right front side for me under the warranty claim as well. I have to take it back for the replacement job next Wednesday and will update everyone here. BTW, he also says it has nothing to do with the regen. braking system.
     
  16. bisco

    bisco cookie crumbler

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    does it have anything to do with overtorqueing the lugs?
     
  17. toyolover

    toyolover Member

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    I don't think so. First, I've re-torqued the wheel nuts with torque wrench. Second, The dealer's foreman banged on the left front wheel while it was up the hoist and we both could hear something was loosen. I think the conclusion on the bearing is valid. Besides, the foreman says he's worked at that Toyota dealership for 26 years and I must take in some credit for that as well. The lucky thing is the replacement will be under Toyota warranty. I'd have to pay for the alignment cost.
    We'll see within the next two days.
     
  18. JC91006

    JC91006 Senior Member

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    Is the alignment necessary?

    SM-N900P ?
     
  19. toyolover

    toyolover Member

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    I would think so because the tie rod end assembly has to be removed from the wheel. The Toyota Service Manual says "If the suspension or underbody components have been removed/installed or replaced, an alignment is needed.
     
  20. JC91006

    JC91006 Senior Member

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    if it's necessary after a warranty repair,you shouldn't have to pay