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Prius briefly starting ICE while braking

Discussion in 'Gen 3 Prius Main Forum' started by Dead12VBattery, Jan 23, 2018.

  1. Dead12VBattery

    Dead12VBattery Junior Member

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    I've noticed that my 2010 Prius sometimes starts up the ICE briefly while braking. It seems to happen almost 100% on the time when passing about 70 kph (43 mph) when exiting the highway on my commute home, which means under the following circumstances:
    • About 30 min of driving 120-140 kph (75-87 mph).
    • Approach exit driving about 120 kph (75 mph).
    • Release throttle to slow down to approximately 100 kph (62 mph).
    • Gently brake to 50 kph (31 mph), with constant pressure on the brake pedal and not touching the throttle.
    • While braking, the ICE starts up at about 70 kph (43 mph) and immediately shuts down again. It can feel this, hear it, and see the fuel usage indicator go up for a brief moment. The car continues to decelerate normally though.
    Is this normal? It seems fairly pointless (though probably harmless). The car is in normal mode (that is, not eco, pwr or EV).
     
    #1 Dead12VBattery, Jan 23, 2018
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  2. bisco

    bisco cookie crumbler

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    what level is the battery at when it happens?
     
    #2 bisco, Jan 23, 2018
  3. Dead12VBattery

    Dead12VBattery Junior Member

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    Usually as full as it gets from normal driving (I think it is 7 bars or so? it's one bar missing)
     
    #3 Dead12VBattery, Jan 23, 2018
  4. bisco

    bisco cookie crumbler

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    it could be burning off some excess charge, but i would think it would be full bars.
     
    #4 bisco, Jan 23, 2018
  5. Dead12VBattery

    Dead12VBattery Junior Member

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    That's an interesting thought, but then I wouldn't expect it to always happen at the exact same speed. It's also noteworthy that this is the same speed that seems to be the maximum for driving purely electric.
     
    #5 Dead12VBattery, Jan 23, 2018
  6. bisco

    bisco cookie crumbler

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    when i had a regular commute in my 2008, at the end of the highway run, fully warmed engine in summer, the last mile on a back road at 20 mph or so would always see the engine come on every time. but the battery was full from the highway.
    not sure if it relates to your situation at all though.
     
    #6 bisco, Jan 23, 2018
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    That's the max speed 3rd gen Prius will run without the engine kicking in. Happens to us everytime we coast down a steep hill.

    That's correct.
     
    #7 Mendel Leisk, Jan 23, 2018
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  8. Maarten28

    Maarten28 Active Member

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    The ICE will always spin when you're faster than 70 km/h, the Prius injects some fuel (making it look like the ICE is starting up) while braking through that speed to let the transition from spinning ICE to ICE off go smoothly.
    This is perfectly normal.
     
    #8 Maarten28, Jan 24, 2018
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  9. jack black

    jack black Active Member

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    isn't EV speed limit 46mph?
    for the record, I don't have that issue OP describes at 43mph.
     
    #9 jack black, Jan 24, 2018
  10. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah. The one place I notice this is rolling down this hill.

    upload_2018-1-24_6-39-41.png

    Pretty much foot off the gas (maybe a slight touch to defeat regen) the car will accelerate, and at the bottom of the hill the limits goes from 60 (kmh) to 80. Somewhere around 73~74 kmh, the engine kicks in. Always.

    Rough conversion from kmh to mph:

    74 x 5/8 = 46
     
    #10 Mendel Leisk, Jan 24, 2018
    Last edited: Jan 24, 2018
  11. Maarten28

    Maarten28 Active Member

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    What the exact speed is is not really interesting. Especially while braking you can not say it will happen at exactly that speed, and european speedometers also have about 8% offset in speed.
    It may also not be so noticable on MPH speedometers because of how the consumption gauge works. On european cars it is usually in liter / 100 km and will indicate nothing when the foot is off the gas and it will blip a few bars when the ICE is turned off.
    On US cars the gauge will stay full bars when the foot is off the gas (99 mpg) and will probably not dip a single bar because the mileage will not drop below 99 mpg.
     
    #11 Maarten28, Jan 25, 2018
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  12. douglasjre

    douglasjre Senior Member

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    Your battery pack is dying
     
    #12 douglasjre, Jan 27, 2018
  13. 4md

    4md Member

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    Mine does the exact same thing, but I'm not sure about the speed, I thought it was at different speed every time, I'll start to observe it.
    I'm pretty sure that's not connected with the battery condition, because mine was dying and I've replaced it and it continued to start the ICE for 1-2 seconds.
     
    #13 4md, Jan 29, 2018
  14. Maarten28

    Maarten28 Active Member

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    No. This is absolutely no indication that the battery pack is dying.
     
    #14 Maarten28, Jan 31, 2018
  15. b100

    b100 Member

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    He's joking maarten:p
     
    #15 b100, Feb 7, 2018
  16. Mendel Leisk

    Mendel Leisk Senior Member

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    The Dutch uncles comparing notes. ;)
     
    #16 Mendel Leisk, Feb 7, 2018
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