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Prius downshifting or slowing down on small hills. Also bucking, or jerking some.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by LeeCincy, Jun 18, 2014.

  1. LeeCincy

    LeeCincy Junior Member

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    Hello all! I am new here and would like to introduce myself. My name is Lee and I have owned a 2007 2nd Gen Prius for about a month in a half. I love my Prius although I purchased it with high miles (just under 200K) I felt a little adventurous and took it on a rather lengthy trip from Ohio to Nebraska and then to South Dakota and back home) a few weeks ago and I've noticed a few things since.

    Before this trip I could let my car coast down slight grades or hills with no issue. The car just coasted like normal which helps save gas of course. Well now on slight hills it feels as if the car is down shifting. It actually slows itself down slightly. On steeper grades it will still coast but up until a few weeks ago I could literally coast on a slight grade. Not so anymore.

    Also when I accelerate now sometimes when I lift my foot off the accelerator it bucks or jerks. It's not very violent but noticeable. I didn't experience any of these issues before the trip. I was wondering if the rocky back gravel roads of Nebraska could be a contributing factor in any of this or perhaps the steep hills of Rapid City South Dakota (SD was when I first noticed the reduction in coasting)

    I've been in to see the Toyota Service department In my area and of course they told me that, "Those Prii just drive like that". I refuse to accept that since I am very sensitive to changes in drivability in any vehicle that I own and I know that my Prius operates and feels differently than it did before. Any help would be greatly appreciated!

    -Lee
     
  2. nh7o

    nh7o Off grid since 1980

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    Welcome to PC.

    The first thing you will find is that service departments only operate on the basis of diagnostic trouble codes, and then use charts after that to replace parts until the codes are gone. So if your car has no codes, then it is perfect and there is nothing they can do.

    I would check for alignment issues and brake drag. Take off the wheels and make sure all is well with the slide pins (corrosion, grit, etc), and see if each wheel spins freely. An alignment shop will run a test for a small cost, and you can post the results here to determine if it is too far out. Check your tire pressures, they can be 40 psi or more for best coasting.

    Make sure you are not in B mode on the shifter. Always use D unless the hills are long and steep. Also, make sure the engine is shutting off when you are gliding. If the engine is staying on, which can happen due to a problem (like a failed 12V battery) then the car can have that laggy feel.
     
    #2 nh7o, Jun 18, 2014
    Last edited: Jun 18, 2014
  3. goldfinger

    goldfinger Active Member

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    I wonder if the plugs were ever changed?
     
  4. edthefox5

    edthefox5 Senior Member

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    Tire pressure
    Spark plugs & while in there ignitor tip corrosion inspection
    Throttle body clean
    Tran fluid change
    Inverter coolant change
     
  5. uart

    uart Senior Member

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    Lee, it sounds like you're driving in "B" mode instead of "D" mode on the transmission.
     
  6. LeeCincy

    LeeCincy Junior Member

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    Thanks for the fast reply goldfinger,edthefox5, and uart. Thanks Uart but I've only used B mode on a few occasions and that was when I was going down a very steep hill. I drive in D exclusively. I think I'll make a check list with the items that edthefox5 mentioned and start there. Thanks to you all for the help!


    iPad ?
     
    edthefox5 likes this.
  7. tanglefoot

    tanglefoot Whee!

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    I think on some really long, steep descents, I've had the engine rev up almost as if it were in B mode. I believe that even in D, when the traction pack reaches maximum charge, the system might use some B-mode behavior to bleed off electricity. This probably wouldn't happen on slight hills though. Does the speed of the gasoline engine actually increase as you descend (you can tell by the noise/vibration), or is there just a feeling of resistance?
     
    #7 tanglefoot, Jun 18, 2014
    Last edited: Jun 18, 2014
    Mendel Leisk likes this.
  8. LeeCincy

    LeeCincy Junior Member

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    I don't think the speed is increasing at least I don't hear any increase noise or feel vibration. I'm about to drive it now and will listen. Thanks tanglefoot


    iPad ?
     
  9. nh7o

    nh7o Off grid since 1980

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    That is indeed the case. If the descent is long, the engine will be completely off, but will start revving when the battery fills. It does not rev as high as when B mode is selected, however. In fact, I have taken to using B mode much less, as the 4000RPM produced seems just too frantic for the small increase in drag produced. I think in the long run it is easier to replace the brake pads than the engine.
     
  10. uart

    uart Senior Member

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    Yep, D mode doesn't start revving the engine to burn off excess charge until it's right up at the very top level of the 8th bar. In "B" mode it basically spins the engine all the time, but really starts turning up the revs to a noticeable amount when the SOC is in upper region of the 7th bar. It seems to progressively increase the revs as you go from 7 to 8 green bars.

    Yeah it can really get that little engine screaming on a long descent, that's for sure. It can be pretty disconcerting the first time you hear it.

    Despite that I'm using "B" mode more than ever for long descents these days, because I think it makes it a bit easier on the HV battery and mine is definitely showing it's age. I think my engine will easily outlast the HV battery.
     
  11. nh7o

    nh7o Off grid since 1980

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    OK uart. Using Priidash and watching charge amps, I see that in either of the two modes, the charge current goes to very low values when the charge is at all green bars. The only difference is that there is a need to use more friction braking in D mode. So one or the other does not make that much difference on the battery. Even if the shift is made to B mode proactively, at the top of the hill, then the battery still gets to the same level of charge. At least here, where I go up and down 1000m in elevation each trip.
     
  12. uart

    uart Senior Member

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    Yep, if the descent is large enough. Around here the hills aren't that large (well at least most of them aren't) but there's lots of them. My battery gets some funky behavior (undershoot) after the battery has been charged to 8 bars, but it's usually ok if it's only 7 bars. I actually use "B" mode to prevent me getting all 8 green bars on the modest sized hills where I drive.

    BTW. With this undershoot the battery ECU gets confused or something about the state of charge. After it goes to 8 green bars it (soc) stays high for a quite a while, but then suddenly plummets to 2 or 3 bars with virtually no discharge occurring. It's really annoying and I often think this battery can't last too much longer, though it has been this way for nearly 2 years now and is still going.
     
  13. JC91006

    JC91006 Senior Member

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    I wonder if a battery module would go bad if you let the car sit for a couple weeks? like a weak 12v that sits for a period of time.

    I worried about my 2005 going out, couldn't take the suspense anymore, bought myself a newer battery and replaced it today. Mine doesn't undershoot but the time factor was making me nervous

    SM-N900P ?