Full Battery & going downhill - Engine coming on?

Discussion in 'Prime Technical Discussion' started by SeattleHawaii, Jan 27, 2017.

  1. SeattleHawaii

    SeattleHawaii Member

    Joined:
    Jun 26, 2014
    47
    56
    0
    Location:
    Seattle, Wa & Papaikou, Hi
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Hi folks - 2500 miles on my prime after over 2 months driving. Loving it 100% no complaints here! One question that I had...if the battery is 100% full and one goes downhill, hitting the brakes and hence filling the battery...I noticed today that my ICE turned on in two occasions...is that to be expected? I was in EV (not EV auto) mode.
    thanks much for any insights.
     
  2. mr88cet

    mr88cet Senior Member

    Joined:
    Sep 9, 2008
    2,002
    1,166
    0
    Location:
    Austin, TX
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    My guess would be that it's kicking in engine braking like "B" does on my Gen-2.
     
  3. SeattleHawaii

    SeattleHawaii Member

    Joined:
    Jun 26, 2014
    47
    56
    0
    Location:
    Seattle, Wa & Papaikou, Hi
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    that was my thinking...it doesn't do it always...I have a slight hill going down from my house when the car is fully charged and haven't noticed it yet. Today's hill was a bit steeper though...
     
  4. David Beale

    David Beale Senior Member

    Joined:
    Jul 24, 2006
    5,963
    1,939
    0
    Location:
    Edmonton Alberta
    Vehicle:
    2012 Prius
    Engine is on without burning fuel. Watch the display to see that no fuel is being used, then it's engine braking for sure.
     
  5. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    86,343
    38,237
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    does it go through the whole warm up cycle?
     
  6. SeattleHawaii

    SeattleHawaii Member

    Joined:
    Jun 26, 2014
    47
    56
    0
    Location:
    Seattle, Wa & Papaikou, Hi
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    the display did stay in EV mode, meaning it showed the EV acceleration, however the range didn't go down driving and the mpg's changed from the usual 199.9 to a lower mpg showing that the engine obviously was on..went back to EV after a minute or so...
     
  7. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    86,343
    38,237
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    a minute isn't full warm up, even in warm weather, so that's good.
     
  8. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    86,343
    38,237
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    try ev auto and see what happens.
     
  9. 'LectroFuel

    'LectroFuel Senior Member

    Joined:
    Feb 3, 2016
    880
    668
    0
    Location:
    San Juan Capistrano, CA
    Vehicle:
    2016 Prius
    Model:
    Four
    How is the engine on without burning fuel?o_O:confused:
     
  10. 'LectroFuel

    'LectroFuel Senior Member

    Joined:
    Feb 3, 2016
    880
    668
    0
    Location:
    San Juan Capistrano, CA
    Vehicle:
    2016 Prius
    Model:
    Four
    I go down a large hill everyday and the battery gets full. It's normal. The battery doesn't want to overcharge and therefore doesn't want to use the regenerative brakes. When I stop at the bottom of the hill, the engine revs pretty high. There are probably better ways this could be done because I'm always thinking in my head "I'm wasting gas going downhill! There's no more room in the battery!"
     
    citiprius likes this.
  11. David Beale

    David Beale Senior Member

    Joined:
    Jul 24, 2006
    5,963
    1,939
    0
    Location:
    Edmonton Alberta
    Vehicle:
    2012 Prius
    The HSD spins the engine without injecting fuel. You have to be moving, of course, and above a minimum speed for this to happen. You can see you aren't burning fuel by mileage displayed, and if you have a "Scangauge" you can see the fuel being used "instantly" (with about a 1 sec. delay). The "normal" Prius does this to keep control when descending a hill with the battery "full", and you applying the brakes gently. "Full" meaning it doesn't want to charge the battery any further. Computers understand differently than we do. ;)
     
    'LectroFuel likes this.
  12. Captmiddy

    Captmiddy Active Member

    Joined:
    Dec 15, 2016
    225
    202
    1
    Location:
    Massachusetts
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    I had this happen yesterday, went down a hill and at the bottom the engine came on and it stayed on through the likely normal warmup cycle. It didn't go back to EV mode for 5 minutes. I did not have a full charge at the top of the hill, I was below 20 Mile range, but while the engine was on I started gaining range. It was almost like it was on charge mode. This same hill in the other direction causes the engine to come on going up so I am just going to consider this the Prime Curse Hill :D.
     
  13. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    86,343
    38,237
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    yes, that was definitely the warm up cycle. o/p's description of one minute, and average mpg's going down might be something new toyota has come up with, or just an error.

    for anyone leaving there home and going downhill that fires the engine on a regular basis, the only solution on the pip was not to fill up the battery all the way when charging.
     
  14. Sam Spade

    Sam Spade Senior Member

    Joined:
    Dec 3, 2016
    2,036
    997
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    You connect the engine to the wheels......and then don't feed it any (or just a tiny bit) gas.
    That is the definition of engine braking.
     
    'LectroFuel likes this.
  15. SeattleHawaii

    SeattleHawaii Member

    Joined:
    Jun 26, 2014
    47
    56
    0
    Location:
    Seattle, Wa & Papaikou, Hi
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    hmm...maybe it was closer to 5 min....
     
    bisco likes this.
  16. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    86,343
    38,237
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    it's hard to remember if it's not something you're not concentrating on at the time.
     
  17. 'LectroFuel

    'LectroFuel Senior Member

    Joined:
    Feb 3, 2016
    880
    668
    0
    Location:
    San Juan Capistrano, CA
    Vehicle:
    2016 Prius
    Model:
    Four
    Oh, I never knew that the HSD could power the engine at such high RPMs, interesting. Why doesn't the regenerative braking stop "regenerating" when you take your foot off the gas and the battery is "full?"
     
  18. Lee Jay

    Lee Jay Senior Member

    Joined:
    Jun 25, 2009
    4,924
    3,554
    0
    Location:
    Westminster, Colorado
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    It does - it's using the engine's pumping losses to dissipate energy (turns the kinetic energy of the car into heat in the air).
     
    'LectroFuel likes this.
  19. 'LectroFuel

    'LectroFuel Senior Member

    Joined:
    Feb 3, 2016
    880
    668
    0
    Location:
    San Juan Capistrano, CA
    Vehicle:
    2016 Prius
    Model:
    Four
    On my gen 2, the green arrows are going from the wheels to the electric motor to the battery when the battery is full, so I thought it was trying to charge the battery still. I just learned a lot about a car I've had for almost 12 years:LOL:. thanks!
     
  20. jdonalds

    jdonalds Active Member

    Joined:
    Mar 13, 2008
    539
    224
    0
    Location:
    Redding, California USA
    Vehicle:
    Other Electric Vehicle
    Model:
    Touring
    That's normal behavior. Once you've used the motor-generator to fully charge the battery the extra regen energy has to go somewhere so Toyota kills the motor-generator by making the engine take the role.
     
Loading...