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Unusual problem while going downhill with cruise control

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by royvogel, Feb 19, 2012.

  1. royvogel

    royvogel TanzMan

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    Anyone have any ideas? Twice now, while going downhill hill (steep grade on freeway) my Prius has revved up to over 4,000 RPMs with the cruise control set at approximately 65 mph. The noise of the engine was my tipoff and I immediately had to turn the cruise control off. This just doesn't make sense to me! Seems like this could be a potential problem for those of us utilizing cruise control!!!
     
    #1 royvogel, Feb 19, 2012
  2. cwerdna

    cwerdna Senior Member

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    How "full" does the HV battery look when this happens? If it's at or near full, it's normal. The car will basically put itself in B mode to do compression braking w/the ICE to keep the HV battery from getting overcharged.

    I used to hit this very frequently where I last lived (would go down a fairly long downhill grade on the way home). I've hit this on certain freeway trips in hilly areas too. Cruise control doesn't need to be on for this and I never use it on the former route.

    Since I have a ScanGauge II, I can monitor the ICE RPMs as well as HV battery SoC. It on cue when the HV battery is very close to 80% SoC (represented as "full" on the 2nd Prius' MFD).
     
    #2 cwerdna, Feb 19, 2012
  3. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    The Gen 3 will work not to gain speed going downhill with the cruise control on. (Gen 2 just goes faster and faster)

    When you choose B mode or when the HV Battery is as charged as the computers want it to be, the car will use engine braking to slow your speed when you brake. This avoids overheating the friction brakes, which would be bad.

    Your Cruise Control had filled the HV battery and was still needing to lower your speed. Isn't it great the car tries to never leave you without brakes?
     
    #3 JimboPalmer, Feb 19, 2012
  4. Zanrok

    Zanrok Casual Prius Lover

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    yup yup, I was just gonna say the same thing. I notice that when I am going down steep hills and I engage B mode, and the battery is near full or full the engine will make that terribly loud noise like you described. lol

    I would say its engaging B mode while in Cruise.
     
    #4 Zanrok, Feb 19, 2012
  5. royvogel

    royvogel TanzMan

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    Well then, my Prius is smarter than me! Thanks to all for your valuable feedback! You guys and this site are awesome!
     
    #5 royvogel, Feb 19, 2012
  6. kevinwhite

    kevinwhite Active Member

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    The Gen 2 does the same thing - it may not be as aggressive as the Gen 3 in the use of engine braking.

    kevin
     
    #6 kevinwhite, Feb 19, 2012
  7. cwerdna

    cwerdna Senior Member

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    #7 cwerdna, Feb 19, 2012
  8. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    There are a couple areas in which the Prius makes you rethink your previous experience with other cars.

    Auto A/C: This is more than just giving you cold air. The Prius uses a combination of cooling, heating, vent control and fan control to maintain the desired cabin temperature.

    Cruise Control: Better thought of as "speed control." As we've seen here, the Prius does not only keep you at a minimum speed as set, it will make sure you don't race uncontrolled down a steep hill.
     
    #8 TonyPSchaefer, Feb 20, 2012
  9. ImeanGreen

    ImeanGreen Prius v Five BP Brigade #236

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    Is there an RPM meter with the 2011 prius? I'm new to it and didn't noticed it.
     
    #9 ImeanGreen, Feb 25, 2012
  10. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    No there's not. This has been a point of contention for menu Prius owners and one of the main reasons why some have purchased devices that read the CANBUS and display information such as RPM.
     
    #10 TonyPSchaefer, Feb 25, 2012
  11. tumbleweed

    tumbleweed Senior Member

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    Not a problem, it is just doing what it was designed to do, use the ICE to slow the car when the SOC is high. I have seen mine at 5K RPM coming down steep mountains.

    Red line of the engine is 5200 and it will not exceed that. The car protects itself pretty well and 4K or 5K is absolutely no threat to the engine as long as it is warmed up.
     
    #11 tumbleweed, Feb 26, 2012
  12. pjksr02

    pjksr02 Active Member

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    Phew! I thought the runaway Prius had returned! :car:
     
    #12 pjksr02, Feb 26, 2012
  13. tumbleweed

    tumbleweed Senior Member

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    :eek: Please not that again!
     
    #13 tumbleweed, Feb 26, 2012
  14. wjtracy

    wjtracy Senior Member

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    ...my VW minivan does this on hills (RPM speed up), apparently the transmission is downshifting to control speed. Seems unsafe, especially one time happened on an exit ramp.
     
    #14 wjtracy, Feb 29, 2012
  15. qbee42

    qbee42 My other car is a boat

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    Which begs the question: Why were you running CC on an exit ramp?

    Tom
     
    #15 qbee42, Feb 29, 2012
  16. wjtracy

    wjtracy Senior Member

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    ...don't recall exact scenario but hills, and once the downshift gets started sort of seems like you are out of control for a second. Basically I don't use CC anymore on hills for the minivan.
     
    #16 wjtracy, Feb 29, 2012
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