Prius Prime engine running in EV mode?

Discussion in 'Prime Main Forum (2017-Current)' started by PDXNGNEER, Jan 14, 2020.

  1. PDXNGNEER

    PDXNGNEER New Member

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    My 2018 Prius Prime has been acting strangely these past few months, and I'm trying to figure out if it's expected behavior, or if something has changed.

    The issue is that the engine will sometimes run, even though I'm in EV mode, and have a high level of battery charge. I know that the engine will start in EV mode, under certain conditions (e.g. when the front window defroster is on, etc.), but my car is doing it even when none of those conditions are being met. I thought it might be related to the colder winter weather, but I don't remember it doing this last winter at all.

    The typical behavior goes something like this:

    1. Car has not been used for several hours, and has a high SOC (80-90%). Outside temp is generally 40-55 degrees.
    2. Turn the car on and start driving. Climate control is on, but none of the defrosters are. Drive mode is set to Eco and EV (not EV Auto).
    3. Screen may display that the car is in normal EV mode without the engine running ('EV Mode' icon next to the 'ECO Mode' icon, and 'EV' displayed inside the little car icon), or it may display a strange combination of EV and HV mode ('EV Mode' icon next to the 'ECO Mode' icon, but there is nothing displayed inside the little car icon). In the first state, the engine is not running, in the second, it is.
    4. If it's in the second state, there is nothing I can do to get the engine to turn off. It continues to stay on, even when braking, coasting, or just sitting at a light. Turning off the climate control completely, has no effect, either. The energy monitor on the nav system screen clearly shows that the engine is providing power either to the battery, and/or to the wheels.
    5. After driving for anywhere between 5-10 minutes, the car will switch to normal EV mode. This leads me to believe that maybe the engine needs to be warmed up in colder weather, so that it's not potentially switching on and off while it's cold.
    6. The one thing that makes me think that I'm wrong about this is that if I force the engine to start by either a) switching to HV mode and accelerating hard, or b) turning on the front defroster, and then immediately switching back to EV mode, or turning off the defroster, the engine will continue to run for several minutes before finally turning off again. I can do this over and over again, so it's very repeatable.

    If it's actually an engine temperature issue that is causing this behavior, why would it continue to keep happening, once the engine reached some initial threshold temperature? What I'd like to know is...

    1. Has anyone else seen this type of behavior?
    2. Is this expected behavior? As I said, I don't recall it ever doing this last winter.
    3. If it's expected, then what is the purpose behind it?

    Since I live within 12 miles of my office, I can usually get to and from work without using any gas, which is one of the reasons I bought this car. This weirdness is causing me to burn fuel, for what I feel is no reason at all, so I'd like to understand if this is something that I need to have looked at.
     
  2. xray22

    xray22 Junior Member

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    I can't help you figuring out why, but I notice the same thing.
     
  3. Tideland Prius

    Tideland Prius Moderator of the North
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    Let's get one thing out of the way first. Once the engine starts running, it will complete its warm-up cycle until some water temperature threshold is met (to warm up the catalytic converters to reduce emissions).

    Ok The high SOC is what is letting me think that you're going downhill or you're using B mode downhill. That typically kicks the engine on as your high SOC means higher voltage = greater heat into the battery = less regen so if you're in B, it'll kick the engine in to help supplement with engine braking and once it's on.... [see first paragraph].

    It can still happen if you're in D and you brake (and thus increasing the amperage into the battery and all the other conditions in the second paragraph).

    Another possibility that @bwilson4web found is if you use cruise control at a certain higher speed with a high SOC. (I can't remember it now so hopefully he'll chime in). We can't explain this scenario.
     
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  4. PDXNGNEER

    PDXNGNEER New Member

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    I did a lot of reading in this forum prior to posting, and knew that some of those conditions could trigger the engine to run, even with a high SOC. In none of my cases was I using B mode, or using cruise control, so I knew that couldn't be the culprit. The area I live in is pretty flat, so there really aren't any steep hills, so I don't think braking is causing it either.

    The water temperature threshold thing explains some of the behavior I'm seeing, but not entirely. Assuming that first time the engine kicks on, it has to complete it's warm-up cycle before switching to pure EV Mode. That makes sense, but if I immediately force the engine to kick back in by switching to HV Mode and accelerating hard, and then immediately switch it back to EV Mode, the engine continues to run for several more minutes. If it had just completed it's warm-up cycle and achieved the necessary water temperature just seconds prior, why would it need to continue to run? Shouldn't the water/engine/converter already be at the temperature threshold (or very close to it)?

    The car definitely doesn't do this in the summer, but maybe that's because I never turn on the front defroster, thus triggering the engine to start the first time coming off a full charge. I might try to see what happens if I drive with a full charge on a cold day, with the climate control turned off. Maybe if I can avoid that initial cold engine start, it'll stay in true EV Mode the entire time.
     
  5. Tideland Prius

    Tideland Prius Moderator of the North
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    Well it starts cooling down the moment it shuts off, so if it dropped below the temperature threshold, it’ll run the cycle because it’s below (I.e. it doesn’t hack to see how close it is to the threshold just whether it’s above or below). That’s one possibility.

    Or it’s not a single threshold and there’s a grey area where it’ll run even if it has done so before.

    The fact that it doesn’t do that in the summer means it probably is temperature related. It doesn’t cool down as quickly in the summer due to the temperature difference between ambient and the engine.
     
  6. m8547

    m8547 Active Member

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    There are a few factors here.

    Something is triggering the engine to run in the first place. It sounds like that's use of the defroster. If you use the floor+windshield vent setting instead of the defroster button that will give you a light amount of defrosting using the heat pump.

    In EV mode in cold weather, once the engine is warmed up sometimes the car continues to use it. That is especially likely if you have the heat on or on a demanding drive (for example going up a hill on the highway).

    Another factor is, there seems to be a minimum engine on time. The car doesn't like to run the engine for just a few seconds in many cases. Sometimes it will, but after doing that for a few times it will run it for a longer cycle. When you switch from HV mode or defrost back to EV mode with the engine warmed up, it will probably continue running until the car thinks it has run for a long enough time and until it's no longer needed.
     
  7. schja01

    schja01 One of very few in Chicagoland

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    Add me to the list. 29 degrees just driving, only light acceleration, hvac in auto eco no defroster and ice came on through one warmup cycle. Mid showed EV mode the entire trip but the car icon was only a sillouette(sp?) at times. Weird.
     
  8. psusi

    psusi Junior Member

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    The warm up cycle should not be "run for x minutes" but rather "run until temperature >= x". If it hasn't cooled off much, it won't take long to warm back up.

    Then again I've always had plenty of moments in my '08 where I wonder why the stupid engine is still running. Sometimes the car just seems to do what it wants in defiance of all logic.
     
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  9. Prime Alex

    Prime Alex New Member

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    Although this is admittedly anecdotal, we've been noticing that the car tends to revert to hybrid mode, and then go in and out of EV mode, when we hit -12C.
     
  10. Salamander_King

    Salamander_King Senior Member

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    1. YES, all the times, although more often in winter than warmer months.
    2. Expected, maybe not from operators stand point. But certainly I think it's normal.
    3. Only TOYOTA system engineer knows answer to this question.

    The manual covers this "catch 22" situation very simply by stating ICE will run when the system determines that the gasoline engine needs to be started... and under other conditions not mentioned in the manual.

    gas engine starts.png
     
  11. Trollbait

    Trollbait It's a D&D thing

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    That's normal. The heat pump only works down the 14F for heating the cabin; engine heat is needed below that. Then the system will go into hybrid mode if the battery or other components are deemed too hot or too cold.
     
  12. PDXNGNEER

    PDXNGNEER New Member

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    After a week of refusing to turn on the front defroster while driving, I can confirm that preventing the engine from starting that first time after an overnight charge will indeed keep it in true EV Mode. Once the engine is triggered that initial time, it will continue to run for a while, even when in EV Mode. As several people have mentioned here, it's likely related to engine/water temperature, which makes sense. The short story is that this appears to be expected behavior, and I can happily run in true EV Mode by avoiding that initial engine start.

    Thanks to all for the input.
     
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  13. bisco

    bisco cookie crumbler

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    well done!(y)
     
  14. psusi

    psusi Junior Member

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    Wait a minute... the newer cars have a heat pump? My 2008 can only be heated using the engine heat.
     
  15. Salamander_King

    Salamander_King Senior Member

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    Only in Prius PRIME plug-in. This is PRIME thread.
     
  16. psusi

    psusi Junior Member

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    Only the Prime eh? Good to know. Now the question is does Toyota actually sell them outside of CA? For years I kept asking about the plug in and was told that only CA was getting them, I assume because they were being sold at a loss to meet CAFE standards. Toyota's web site "build one" said there are none in my area.
     
  17. Salamander_King

    Salamander_King Senior Member

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    Been sold nation wide since 2017. A large discount in the North East region applied usually makes it cheaper than a regular Prius after incentives and tax credits. Although the availability in the Midwest and South are somewhat limited. Yap, there are FL PRIME owner on this thread... @jerrymildred
     
    #17 Salamander_King, Jan 28, 2020
    Last edited: Jan 28, 2020
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  18. jerrymildred

    jerrymildred Senior Member

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    Yup! Lots of us. Some have managed to buy here. Some travel to the northeast. Some get them used like I did. That's not because of Toyota; it a stupid decision by the only private distributorships in the country -- Gulf States and Southeast.

    Run on over to see Todd (@TampaPrius.com) at Home - Tampa Hybrids Inc.. He has a 2017 Plus in blue right now. Usually, he has about three Primes. I've never met a dealer who cared more about having happy customers. BTW, he doesn't lie on the real price like other dealers. He puts his best price out first.
     
  19. Trollbait

    Trollbait It's a D&D thing

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    The southern Toyota distributors are independent, and don't care for the plug in. Most dealers willing to sell it require you to order it. Many Prime owners in the South went North for their car.
     
  20. psusi

    psusi Junior Member

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    Weird... several years ago I told my dealer I was willing to order and wait for it to arrive and they said they can't even order them.
     
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