ICE turns on inexplicably

Discussion in 'Prime Technical Discussion' started by Stained glass guy, Apr 20, 2021.

  1. Stained glass guy

    Stained glass guy New Member

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    I have explored a similar topic but it did not answer my question. We have a new 2021 Prime and this is the daily scenario. Leave house fully charged. About 3 miles from home I go down a 3/4 mile hill at no more than 35mph. I use B, or not. At the bottom of the hill is a stop sign. After stopping and proceeding on mostly level road the ICE comes on whenever I use the accelerator, even for very gentle acceleration on level road. This continues until I stop for coffee, about 5 minutes. When I get back in, the ICE stays off until I return home later in the day, going uphill all the way. If the ICE were kicking on to prevent overcharging on the regen going downhill, wouldn't it have done so while going downhill? It waits until I am all the way down. It is more of an annoyance than anything, and I am mostly just curious as to the rationale for this behavior. I have tried different drive modes, climate on or off, defrost on or off, and have had this happen regardless of ambient temperature. Thoughts?
     
  2. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Hard to say. I also have a 2021 and regularly leave my house with a full charge and drive 2 miles to the top of a long descent. When I start down I have 96%, and by the bottom I have 100% again without triggering ICE. Even in 90°F temps the last couple of days. I suspect it's because the car was in the garage and the battery temp is nowhere near 90°F.

    Do you have the ability to see the traction battery temperature? If you were just charging prior to departure it might be pretty warm already, which could trigger the observed behavior.
     
  3. bisco

    bisco cookie crumbler

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    sounds typical for toyota plug ins...
     
  4. Stained glass guy

    Stained glass guy New Member

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    I don't think I can see the temp, but here is another piece of the puzzle. If I turn it off at the bottom of the hill, even momentarily, and then restart the ICE does not engage. If it were a temp or overcharging issue this should not effect it.
     
  5. Stained glass guy

    Stained glass guy New Member

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    Do you have a guess as to why it does this?
     
  6. ems2158

    ems2158 Active Member

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    My 2017 did the same thing today. First time,
    under the same conditions you described.
    I don't normally do this route but the engine started toward the bottom of a mile long decline.

    It was a bit odd since i had about 12 miles of electric range remaining.

    The weather here was pretty cold 38° F. I'm guessing the engine started to heat the cabin.

    I didn't have the rear window defroster on.
     
  7. Salamander_King

    Salamander_King Senior Member

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    Yeah, ICE starting no reason (at least to the mind of the driver) is a very usual thing on this car. The car has a mind of its own. It is covered by the manual. LOL

    upload_2021-4-22_13-43-45.png
     
  8. fotomoto

    fotomoto Senior Member

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    Have you tried starting the trip with different levels of SOC? Warm battery vs cold battery?
     
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  9. Stained glass guy

    Stained glass guy New Member

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    It has done it with temperatures ranging from 10 to 60F, so don't think that is a factor. What confounds me is that if I turn the car off, then back on, the ICE no longer does it, so I think it is something independent of charge, temperature, climate controls, regenerative braking, etc. I am thinking it is more of a feature built into the software that serves no useful purpose. What is SOC?
     
  10. Stained glass guy

    Stained glass guy New Member

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    Yeah, I saw that in the manual. Basically it may start whenever, and don't blame us. LOL
     
  11. bisco

    bisco cookie crumbler

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    the pip manual states 14 reasons why the engine may come on, and adds, 'there may be other reasons'.

    prime was supposed to improve on that, and i haven't read the manual, but toyota's mantra is, 'it is a phev, not a bev. the engine is there for more than one reason.
    and they probably know what is best for the car, but it's all so top secret :rolleyes:
     
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  12. PiPLosAngeles

    PiPLosAngeles Senior Member

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    That means it's a warm-up cycle. The battery temp could trigger ICE to start, but once it starts it will run until the engine gets up to full operating temperature, which can take a little bit. Turning the car off and back on stops the warming cycle.
     
  13. fotomoto

    fotomoto Senior Member

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    State Of Charge.

    Try leaving with, say, a 1/2 full batt and see what happens.
     
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  14. Stained glass guy

    Stained glass guy New Member

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    When I turn it off, and then back on again, resetting the warm up, shouldn't it then kick the ICE on again to do another warm up cycle? It does not do this. Once I turn it off, then on, it does not start the ICE unless the battery is low, which can be quite a while. I believe there is probably a good reason for this behavior, I just really am curious as to what it is.
     
  15. Stained glass guy

    Stained glass guy New Member

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    Thanks. I will give that a shot to eliminate another variable.
     
  16. PiPLosAngeles

    PiPLosAngeles Senior Member

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    No. That's not how the Prius is programmed. The warm up cycle doesn't initiate an engine start, it only controls engine shutoff. Once the engine starts it will run until the programmed temperature is reached, but it will not start on its own for the sake of getting the temperature up.
     
  17. Stained glass guy

    Stained glass guy New Member

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    Getting closer to understanding this but am still unclear as to why the engine starts at all. Full charge start, downhill for a couple of minutes, climate off, and when I get to level ground the ICE starts. I get what you are saying about getting to a set temperature point, but I am still scratching my head over the point of using the ICE at all, under those circumstances.
     
  18. PiPLosAngeles

    PiPLosAngeles Senior Member

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    When the car determines that the current being supplied from braking (engine or pedal) will damage the battery, it will use the energy to turn the gas motor instead of charge the battery. That power has to go somewhere.

    On steep, long hills even that strategy doesn't dissipate all of the extra power and it does appear to go to the battery anyway. After a 15-mile descent my Prime was at 100% charge and continued displaying 100% for the next 5 miles of driving or so.
     
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  19. jerrymildred

    jerrymildred Senior Member

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    Finally a right answer. @fotomoto for the win. The ICE starts in order to burn off excess battery charge that occurred after going down a hill with an already full battery. In point of fact, the ICE is not running, it's being spun by the electric motor in order to use up battery charge. But I think I've read that it does use a tiny bit of fuel thus requiring the warmup cycle to complete.

    I'd guess that those five miles were either flat or very slightly downhill. What kind of miles/kWh were you getting in those five miles after the decent? Very small changes in grade make big differences in m/kWh. ;)
     
  20. PiPLosAngeles

    PiPLosAngeles Senior Member

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    A little uphill, actually, with a lot of stop signs. I hadn't been expecting what I saw so I did not reset any trip meters to measure the mi/kWh for that bit of the drive. Based on past experience I would guess about 4.5 mi/kWh or so.
     
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