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ICE turning on for apparently no reason...?

Discussion in 'Prime Technical Discussion' started by pakitt, Jan 16, 2022.

  1. pakitt

    pakitt Senior Member

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    My 2021 Prime has turned on the ICE for apparently no good reason a couple of times, and not even for one of the many reasons listed in the user's manual.

    Let me explain.
    Today, it is 50F/10C outside temp, AC is set to 70F/21C, EV mode + ECO mode selected.
    I drive the first 5 miles of a 7 miles trip with EV light on and all as usual and quiet and nice.
    I reach a moderate, but long slope, reaching 50MPH going downhill. I start braking moderately (about 70% battery is left, used about 30% up to that point) and all of a sudden the ICE fires up and the EV symbol disappears (as it should).
    I drive the next 2 miles at about 25MPH (as I reached the city center), and when I park the car at my destination, the ICE continues to run for a good 10-20 seconds more, until I decide to turn the car off.
    I then turn the car back on 5 mins later, and the car starts regularly in EV mode and keeps it that way all the way back home, even going up hill.

    Something similar, on the same trip on the same road, with the ICE firing up in the same place, i.e., while braking down-hill a couple of days ago, at about the same external temps.

    I have done the same exact road tens of times now in EV mode, and the ICE never once turns on. Not even going up the same hill on the way back.

    What is going on? why does the ICE turn on when the external temperature is nothing to talk home about (a very mild 50F)???
    Is she having issues? or is it all "normal" and the ICE turns on because the battery is maybe too cold to accept regen charge at the rate you get when braking at 50MPH downhill?
     
    #1 pakitt, Jan 16, 2022
    Last edited: Jan 16, 2022
  2. bisco

    bisco cookie crumbler

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    did you just get it, or is this new behavior? long down hills can wreak havoc with ev mode
     
  3. pakitt

    pakitt Senior Member

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    This is a new behavior since getting the car in Mar. 2021 - and I repeat. The battery was 30% used already, so plenty of space to recharge it going downhill. The downhill slope is probably less than a mile long. So I don’t see how that could be an issue and required the ICE to turn on to compensate.
     
  4. Salamander_King

    Salamander_King Senior Member

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    In my experience, the 2021 PP is more prone to start ICE under normal driving conditions than the 2017 PP. The cold temperature makes it even more prone. But I think the behavior is totally normal. I get my ICE started often unexpectedly. The car has a mind of its own and the owner's manual does have the statement covering the catch-all circumstances.
    upload_2022-1-16_21-52-10.png
     
  5. TPP2k18

    TPP2k18 Junior Member

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    IT's too cold for the regenerative breaking. The ICE turns on to bleed off the energy it can't store. Don't believe me. Put it in Neutral in the slope, and when it warms up above 20ish C it won't happen either.
     
  6. Storm88000

    Storm88000 Active Member

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    You mean the ambient temps are too low?
    I didn't think it would matter since for brakes to work they by definition have to convert forward energy to heat via friction. You are saying the outside temp is sort of counter acting the heat from the friction?
     
  7. bisco

    bisco cookie crumbler

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    it's not the brakes, it is the regeneration system in the tranny recharging the battery.
     
  8. bisco

    bisco cookie crumbler

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    in my mind, 50f is way to warm for it to be the cause. i went for a 9 mile drive in 10f the other morning, engine never came on.
    if i hit a good downhill early on, it would have, but not 30% depleted.
    prime is different i admit, and the heat pump may change the dynamics as well
     
  9. vvillovv

    vvillovv Senior Member

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    It happens, it must be one of the weird programming things in the Prime. It's happened to me on the first downhill I get to when it's cold, too. I don't fully understand it yet, but apparently (no real reason for it).
    If you want to get back into EV mode before you get to your destination, just hit the EV/HV button when you get back onto the flat road.
    If it doesn't go right back into EV mode, the car may need to complete it's engine / ICE warmup cycle before it goes back into EV mode again.

    If you can or feel like trying some new stuff to keep the ICE from firing on that hill, go slower at the top so you don't need the brakes while going down it. Or you could get the ICE warmup cycle completed before you go down the hill, that may work too. Try putting the shift lever into B 1/2 mile before you get to the hill.

    There are lots of ways to try to keep the ICE from starting when you don't want it too. Just takes time to learn about which techniques work for you and which ones don't.
     
  10. pakitt

    pakitt Senior Member

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    Today it happened again. Ambient temp 38F/3C, cabin pre-heated to 70F/21C while plugged in, EV mode from the get go. HVAC set to 70F/21C while driving in Auto mode, priority mode to front seats turned on.

    Same road, same downhill after 3-4 miles of regular full EV mode, about 70% batter left. I hit the downhill, reach 50mph from 30mph (limit is 45mph), I start to brake slowly, adding to the braking the car does already regardless when you lift your foot off the gas pedal. And then, bam!, it turned the ICE on - and not to brake, as it was injecting fuel..!

    The car continues to say it is in EV mode, but drives like as if it is in HV mode. I check the energy monitor and it confirms that (energy going from the ICE to the wheels).

    I get to my destination, park the car. For 2-3 solid minutes has the ICE already being running. I wait, and wait, and it doesn't turn off.
    I check the energy monitor, and no arrows are going anywhere. I think, maybe because it is in P (although, I thought, in P it should still charge the battery if the ICE is running; only in N, there is no charging happening). So I put it back in D (while pressing the brake pedal to avoid moving) and the ICE makes a different noise at it is not free-wheeling anymore, but is charging the battery (the energy monitor shows that).

    I think "maybe it is the HVAC requiring the ICE?" So I turn the HVAC completely off. Nothing, ICE still running.
    I press EV Auto, HV mode, EV mode - still running.

    After probably a solid 2.5 mins, the ICE finally stops. It has been running at that point (i.e., since the downhill), at least a solid 5 mins, probably closer to 7 mins. That has nothing to do with warming up the ICE. In the Gen4, even with the HVAC depending on the ICE heat, the ICE would heat up from a cold start in fat less time than that.

    I go and do my errand (about 5 mins), get back to the car, turn it on, EV mode, I turn on the HVAC back to Auto/70F/21C (the ICE doesn't fire up). And then.... I drive like nothing has ever happened, all the way back home in pure EV.
    I even take a different route after the uphill (about half way of the whole trip), that takes me to a faster (55mph speed limit), longer downhill. I brake less, I brake more, along it: nothing, the ICE never turned on once.

    This leads me to believe that the car is doing fine (otherwise it would have started the ICE again; ambient temp was the same) and the time to "heat up" from a full stop (while parked), was about the same as when I first gotten to the downhill earlier on.

    So I am wondering: what technical requirement, does the Prime have, to have the need to turn on the ICE and run it for almost 10 mins, at a mild 38F/3C (because 38F is honestly not *that* cold for a modern car)? What is the trigger of going down a mild downhill, after running in EV mode without issues for the 3-4 miles prior to that, from a total cold start? Why did it not start the ICE from the get go, if it was "that cold"? Or why did it not start the ICE at the first of many smaller/shorter downhills I get in those 3-4 miles prior to hit "the" downhill, where I do need to brake a bit?

    This behavior seems to have absolutely no logic or a clear technical requirement. I am honestly puzzled...

    PS: the one last test I can do is to get the car through a similar route, but at the mid-way point, before going the infamous downhill, turn the opposite direction at the traffic light, and drive down the much steeper/faster downhill and see if the ICE fires up. It should, but I would still like to know why...
     
  11. vvillovv

    vvillovv Senior Member

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    We'd all like to know why the Prime does everything that it's been reported to do.
    Like I mentioned above, my Prime did the same thing on my first downhill with similar temps in EV.
    It's now in single digit and teens temps all day and night here, so I can't do tests for you in my car.
     
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  12. pakitt

    pakitt Senior Member

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    Just checked the manual and, essentially, EV mode is not a guarantee that the ICE will not turn on, and the reasons why the ICE will turn on are sort of "randomly":
    image.png
     
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  13. pakitt

    pakitt Senior Member

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    Well, if I was worried about the car being "broken" now I know that is just some of that Toyota engineer's weirdness...
    I find interesting in the manual the statement that the ICE will turn on "When the temperature of the hybrid system is low."
    I would then expect the ICE to turn on as soon as I turn on my car from a complete cold start (i.e. after a full night), instead it does that after 3-4mi of EV driving, at the first downhill when I brake "too much"... :D
     
  14. vvillovv

    vvillovv Senior Member

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    It turned on for me without braking, but I hit the crest of the hill at 25 in a 35mph zone and wanted to gain speed in the downhill (no traffic around) since most other drivers do 45 to 55 there and miles more in both directions. I might have asked the Prime to speed me up faster than the battery at it's current temperature could supply the motor with. Still don't know exactly why.
     
  15. eow

    eow Member

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    I am starting to accept that greater minds than my own have programmed my 2022 PP and I should drive it rather than try to understand it. But I am still curious!


    iPhone ?
     
  16. bisco

    bisco cookie crumbler

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    ah you newbies! us pip owners have suffered through this for 10 years :mad:
     
  17. eow

    eow Member

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    I suspect that the climate control is a significant factor on the behaviour of the ICE based on my experimentation this morning.

    I typically have my interior temperature set at 22C and with ambient temperatures below -15C my Prime never goes into EV, rather it is in hybrid mode.

    This morning the ambient temperature is -20C. I reduced the interior temperature selection to 15C and selected Auto. The Prime immediately went from hybrid to EV and no matter how hard I was on the accelerator petal it remained in EV.

    I then started increasing the interior temperature selection. At 17C it went back to hybrid mode.


    iPhone ?
     
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  18. pakitt

    pakitt Senior Member

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    And today she did it again...!
    48F ambient temp. 70F AC setting. EV mode. After 5.5mi driving on the same route as ever, mostly uphill, I hit the downhill, I start picking up speed, reach 50mph, I start gently braking to slow down to 40mph, and bam! the ICE starts. At the first traffic light I reached, I turned off the car, restarted it and the ICE never again turned on and used the battery down to 39%.
    What is going on? What is the very specific condition that turns on the ICE at the same exact point. It wasn't even that cold.
    I don't get it. And it cannot be a fault or a technical problem, because it happens always at the same place, on the same route, but not on other routes. (at least that I could notice).
     
  19. bisco

    bisco cookie crumbler

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    try the same thing in similar weather with a half filled battery
     
  20. vvillovv

    vvillovv Senior Member

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    And/or stop using the brake pedal going down the hill. There are other ways to slow the car going downhill.
    Fun Facts: The most efficient time for the ICE to fire is going downhill.
    And you can learn how to get the Prime back into EV mode without shutting the car OFF, with a bit of practice and patience.
     
    #20 vvillovv, Feb 7, 2022
    Last edited: Feb 7, 2022