Can a Gen 4 prius run out of its hybrid battery in ignition on mode

Discussion in 'Gen 4 Prius Main Forum' started by Alkanator, Jul 18, 2021.

  1. Alkanator

    Alkanator New Member

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    I once left it in ignition on mode till the battery reached two bars, I got nervous that the car would die on me and not turn on its ICE so I put it on ready mode. The engine turned on the moment I kept it on ready mode so I guess that the battery was near empty?
     
  2. jdenenberg

    jdenenberg EE Professor

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    Your Prius will not let the HV battery get "empty". It will usually start charging at 40% with no request for motive power (earlier if you as it to accelerate) and with no bars is still at 20%. There will always be some reserve power to start the ICE unless there is a problem with your Prius.

    JeffD
     
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  3. PaulDM

    PaulDM Active Member

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    Nope. Charging circuit kicks in at 20%
     
  4. bisco

    bisco cookie crumbler

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    do not use ig on mode, put it in ready to avoid catastrophe
     
  5. ChapmanF

    ChapmanF Senior Member

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    In ignition ON mode (unless Gen 4 really drastically changed something), the hybrid battery isn't even in the game.

    Nothing that happens in ON mode happens to the hybrid battery.

    You can definitely discharge the 12 volt aux battery that way, though.

    If the hybrid-battery bar graph changes at all while the car is in ON mode, that's just the battery ECU revising its opinion of how charged the battery is. It isn't the battery really gaining or losing charge, because in ON mode it doesn't.

    Again, unless there is something about Gen 4 that is absolutely different in this respect from all other Prii.
     
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  6. jerrymildred

    jerrymildred Senior Member

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    Welcome, @Alkanator.

    Apparently the 1st three responders missed that you had it in ignition on mode. As usual, @ChapmanF nailed the answer. As with previous generations, leaving the car in ON or ACC will kill the 12v battery. The traction battery is isolated by a relay unless you put the car in READY. Leaving the car in ACC or ON for more than a very few minutes is a really really bad idea. If you leave it in READY, the traction battery will keep the 12V charged and, if the traction battery gets below a certain point, the ICE comes on and charges the traction battery.
     
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  7. Alkanator

    Alkanator New Member

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    I'm pretty sure that the ON (not ready mode) uses the hybrid battery because as I said, the amount of bars inside the battery on the infotainment and/or the Mid decreases once in a while. Btw the air con doesn't work in ignition on mode, just the fan which blows warm air.
     
  8. jerrymildred

    jerrymildred Senior Member

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    Any occasional change you might see to the traction battery SOC when not in READY mode is just the system updating its information from the sensor wires.

    I'm absolutely 100% sure that neither ON nor ACC use the traction battery. I highly doubt that you'll find anyone here who would agree with you. That's why the car shuts itself off to protect the 12V battery after 20 minutes to an hour in ON or ACC depending on which mode you're in. The relay only connects the traction battery to the car in READY mode. If you pay attention, you'll probably hear that relay when you put it in READY, but not in ON or ACC. Anything that runs in ON or ACC is coming from the 12V battery.

    Screen Shot 2021-07-24 at 9.05.20 PM.png
     
  9. bisco

    bisco cookie crumbler

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    'decreases once in awhile' doesn't give us much information. doesn't gen 4 shut off after 20 minutes in ig on mode?
     
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  10. ChapmanF

    ChapmanF Senior Member

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    You have observed that correctly, and the reason is that the air con compressor runs on high voltage from the hybrid battery, which is never connected except in READY mode.
     
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  11. Alkanator

    Alkanator New Member

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    I still wonder how the 12v battery is still working lol. Once I sat with the stereo at 32 volume and the "air con" on for 15 minutes
     
  12. bisco

    bisco cookie crumbler

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    you have the 'special edition' battery :p
     
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  13. jerrymildred

    jerrymildred Senior Member

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    Only the HVAC fan was on. As @ChapmanF said, the compressor runs on high voltage from the traction battery, which is only connected in READY mode. If you look at the manual, it says that the car will shut off after 60 minutes in ACC mode (which lets the fan motor run) and further states that that "cannot entirely prevent" the 12V battery from discharging. It doesn't say that it will discharge the battery every time. Who know what loads you're running or how charged up the 12V is when you do that.

    If you want to sit in the car with AC, radio, etc, do it in READY mode. Your wallet will thank you. And do not neglect the owners manual for this car. It's not just a kneeling pad like most car owners manuals. Read up on it and you'll be seriously happy with your car.
     
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  14. alanclarkeau

    alanclarkeau Senior Member

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    1. With POWER ON - it's ready to drive, the A/C works, the Hybrid battery is in action, the 12v is being force-fed as required by the Hybrid Battery, and if parked for an extended time, PETROL is used by the ICE to keep the Hybrid battery topped up.
    2. With ACC - nothing much happens - but some electrical gadgetry still works - it can FLATTEN the 12v, but the Hybrid Battery couldn't care less!!
    If you have DRLs, you'll want them off when parked with POWER ON and A/C running:

    You need to stop, shut down, and restart WITHOUT changing from "P", the DRLs won't come on till you select a gear.. If you decide to reverse/fwd 6" to get a better alignment, the DRLs come on again - start the process again.

    This was an article about it in relation to going to the Drive-In:

    Going to the drive-in | PriusChat
     
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  15. ChapmanF

    ChapmanF Senior Member

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    It looks like you have condensed the four power states into only three. There are four.

    • OFF - nothing much has power, except ECU memories, smart key transceivers, dome lights, horn, head/taillights if you turn them on, etc. Stuff like the brake system or evap system self tests can run while OFF, or the brake pump start when the driver's door opens.
    • ACC (foot off brake, one button push) - most stuff still off, except for the infotainment system.
    • ON (foot off brake, two button pushes) - most 12 volt stuff in the car is powered. The dash display and most warning lights are on. HVAC controls will work and the blower will run. Not ready to drive, the A/C does not work (except for the blower), the hybrid battery is not in action, and the 12 volt battery is not being charged. In fact, ON discharges it faster than ACC does, because more of the car is powered.
    • READY (foot on brake, button push) - The word READY is shown on the dash. It's ready to drive, the A/C works, the Hybrid battery is in action, the 12v is being force-fed as required by the Hybrid Battery, and if parked for an extended time, PETROL is used by the ICE to keep the Hybrid battery topped up.

    In sum, as mentioned earlier in the thread, the hybrid battery is not connected in any state except READY.
     
  16. alanclarkeau

    alanclarkeau Senior Member

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    Yep - I forgot about the "2 PUSH" mode - I've never used it, couldn't see any point in it - I only ever use 1) OFF (obviously) and 2) "READY". There has never been a time here where I wanted it ON without A/C - but I suppose it could happen.
     
  17. ChapmanF

    ChapmanF Senior Member

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    ON is used in a lot of diagnostic procedures; all the ECUs have power then and will communicate with Techstream.

    It's also handy if you realize you've forgotten to roll up the windows.
     
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  18. alanclarkeau

    alanclarkeau Senior Member

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    Ahh - if that happens, here in Australia we just long press the LOCK button to roll up all the windows - something I think was missing in USA.
     
  19. Salamander_King

    Salamander_King Senior Member

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    Just to throw a monkey wrench into this discussion of ON mode, I just found out on all new Japanese (note this may be only on Japanese models) Toyota Aqua (aka Prius C), which is now equipped with an AC100V/1500W inverter system, there is a special ON mode operation to let one use the AC100v outlet in the car continuously with occasional engine kicking on as needed. Yes, the Toyota Japan site says a tank full of gas would provide 5 days worth of electricity to the average Japanese home on this special ON mode.

    AFAIK, none of the US models of Prius or any other Toyota hybrids has this functionality, but if it comes to the US... there will be an all-new use of ON mode.

    The following linked page explains the procedure on all new Japanese Aqua, but it is in Japanse.
    トヨタ アクア | 特長 | トヨタ自動車WEBサイト
     
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  20. ChapmanF

    ChapmanF Senior Member

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    There was another recent thread about that new Aqua, where the announcement mentioned a new "emergency power supply mode", which I took to be a way you could get the car "READY-like" for use of the inverter, without it automatically shutting down or letting passers-by drive it away.

    I did not see any owner's manual excerpts to see exactly how one gets into the "emergency power supply mode". I would probably talk about it as a distinct mode from ON ... technically it is more "READY with limitations" than "ON with extras".

    Already in some Gen 3s was a "remote A/C" mode that is a kind of "READY with limitations", in which the air conditioning works.
     
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