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When the Prius Runs out of Gas

Discussion in 'Gen 3 Prius Main Forum' started by iskoos, Dec 14, 2019.

  1. iskoos

    iskoos Active Member

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    Not trying to run out of gas and get stranded but I am just curious. What exactly happens when the Prius runs out of gas and the car tries to start the gas engine with no success?
    Does it try several times and quits and give you some warning?
    Do you feel the car tries to start the engine but ICE doesn't start?

    I would especially like to hear this from those who experienced it (intentionally or unintentionally) first hand.

    I read the thread by Bob Wilson. He says the car silently switches to traction battery and runs it down. But I am thinking the car should try to start the engine several times at least before giving up and we should feel it.

    I would like to know a little more detail if possible.

    Thanks
     
  2. Dxta

    Dxta Senior Member

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    One of the signs you're out of or running out of gas is when your fuel indicator gets to the reserve level. At this point, your car is warning you to go get some fuel, or you'd be stranded, if you ignore.

    The car would also suddenly stall.
    A continued starting of the car would total discharged the battery pack.

    Finally, don't ever get your gasoline levels to a point where it starts showing the reserve or near empty indicator light on
     
  3. Grit

    Grit Senior Member

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    ICE either starts up with enough voltage, or doesn't spin/start up at all due to low voltage and/or if HV is in a protected mode. You will never feel it like a car w/a starter trying to turn over.
     
  4. Grit

    Grit Senior Member

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    When DTE is 0, you have about 2 gallons left in the tank. There is no reserve level, it's just an indicator of low gasoline fuel. I drive 50 miles after DTE = 0 at times but no further than that.
     
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  5. fotomoto

    fotomoto Senior Member

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    I haven't done it in a Prius on purpose but I did in a C-Max as part of a forum fuel economy challenge. The last few miles, I carried a fuel can and drove a loop around several gas stations. Anyways, the ICE just stops; no sputters, no retry starts, etc. and one is left with the remaining SOC in the HV battery for propulsion.

    YMMV.
     
  6. fuzzy1

    fuzzy1 Senior Member

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    I believe that if the car made start attempts that could be felt, Bob would have reported it. The lack of any such obvious shutdown indication in the Gen3 was one of his complaints, and a reason for starting that thread.
     
  7. iskoos

    iskoos Active Member

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    So you are saying the car doesn't make attempts to start the ICE.
    Then this begs the question of "How could the car know it used the last drop of gas in the tank?"

    I mean the fuel level indicates "No gas left in the tank" and the car drives 100+ miles easily. If the car stops trying to start the ICE, it should know that it ran out of gas somehow. The reason cannot be the fuel level sensor as it is utterly inaccurate.
    Could it be the fuel pressure? I will say maybe ECU checks the fuel pressure and when it sees it is down, it determines that it ran out of gas and doesn't make attempts to start the engine. But the same can easily happen when a fuel pump goes out or say there is a leak in the fuel line.

    So I hope I am able to explain myself. It really makes me wonder what hints ECU that it truly ran out of gas that it doesn't even try to start the ICE.

    Sorry for digging this issue; It is just my curiosity.
    Thanks
     
  8. Johnny Cakes

    Johnny Cakes Senior Member

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    That's my squeal number - 50 miles after DTE is zero (easier to use DTE then happen to see the flash of the last pip). I figure I always get at least in the 30's MPG and I don't go up any steep hills, so I figure that 50 miles should be very safe.

    If anyone disagrees with that analysis (not the running it down part, just the having 50 miles part), PLEASE reply!!
     
  9. fuzzy1

    fuzzy1 Senior Member

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    No, not necessarily. Rather, if it does make such attempts, they are not necessarily readily felt. I know that I don't feel every successful restart of the ICE in mine from normal auto-stops, so unsuccessful restarts could also be hidden or go unperceived.
     
    #9 fuzzy1, Dec 15, 2019
    Last edited: Dec 15, 2019
  10. MelonPrius

    MelonPrius Senior Member

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    Unfortunately, I ran out of gas just before my last fill up. I had family visiting over Thanksgiving and someone returned my Prius to me with the red fuel light on.

    At some point during my route, the engine didn't respond to the gas pedal but the car was moving (quietly). No matter how fast I tried to go, the car wouldn't go faster than ~15 mph. I was able to get within 30 yards of the gas station and I pushed the car the rest of the way to the pump.

    So as per what Bob W wrote, the ICE silently switches to the traction battery, which is used until it is drained.
     
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  11. iskoos

    iskoos Active Member

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    Well I do feel every time the ICE starts up. And I feel most of the time it shuts off. And there isn't anything wrong with my car. I have driven two other Gen3 Prius and they both felt the same.
    Perhaps it may go unnoticed to some drivers but not to me:)
    So if the car makes several consecutive attempts to start the ICE, and fails, I will catch that immediately.
     
  12. Grit

    Grit Senior Member

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    Never heard of that before, nor seen it.
     
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  13. iskoos

    iskoos Active Member

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    Thank you very much for sharing that. I do believe that "running out of gas" is a stealth operation on Gen3 Prius.
    You don't put the seatbelt on, she beeps, you put her in reverse, she keeps beeping, something goes wrong in the emission system, half of the lights on dash come on. But when she runs out of gas, nothing happens. Did Toyota miss something here?:rolleyes:

    Furthermore, the car lets you drive till you deplete the HV battery down to dangerous levels. And if you do this, you will most likely not be able to start the car even after putting gas.
    I learned all this out. Thanks again.

    Though my follow-up question remained unanswered: How does the car know, it ran out of gas?
    I will patiently wait for some answers.:)
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    I'm sure I read they'd stopped that for 3rd gen. I'd hope that's not true, that's bonehead mode. :mad:
     
  15. Johnny Cakes

    Johnny Cakes Senior Member

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    Well, we are sort of talking apples and oranges. You feel it every time the ICE starts up. But you are asking about what it feels when there's no fuel and the ICE tries, but doesn't start up.

    Well, she did beep at you a hundred miles earlier telling you that she was close to running out and respectfully requesting a trip to the gas station. And she did flash a light on the dash at you. Since you ignored her, maybe she's just getting even by not mentioning it again. :)

    I'm guessing lack of fuel pressure, but I'd be interested in the answer to that also. The car must know because otherwise it would just keep trying to start the ICE over and over again.
     
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  16. fuzzy1

    fuzzy1 Senior Member

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    I feel many spin-ups and -downs, but not all, some road surface conditions on my routes mask it.

    But starting and stopping fuel flow / ignition / power production on a continuously spinning engine? No, I usually miss that.

    It isn't clear to me that when fuel runs out, that the engine does or even needs to halt then restart spinning for start attempts. In fact, if this happens at 46+ mph (Gen3 liftback), I know that the ICE won't stop spinning through the whole attempt sequence, or even after. It keeps spinning to protect MG1 from overspeed. Below 46 mph, I can also easily imagine it continuously spinning throughout the attempts, then do a single standard auto-stop after it has given up trying. It needn't be anything like a common non-hybrid starter engagement to briefly crank the ICE.

    The control ECUs sense and know the ICE and MG1/2 torques and power productions and cylinder misfires, so therefore know when the ICE is not successfully burning fuel. I don't know what additional sensors are in place to sense the presence or absence of fuel.

    As Johny Cakes mentioned, it did beep a hundred miles back. And it beeps again every subsequent time the car is started.

    But lack of other notice was one of the reasons BobW started that thread, and titled it with [WARNING]. His older Prius gave much better notice.
    That sounds like what the Gen2 did, numerous drivers did deplete their traction batteries. But it conflicts with BobW's Gen3 experience. At least with his particular car, Gen3 shut down propulsion earlier, preserving enough battery charge for sufficient future restart attempts. He was never unable to restart the car after adding fuel.
     
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  17. iskoos

    iskoos Active Member

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    I wondered what happens when the car runs out of fuel. And the answers I got telling me that it just switches to EV mode silently. (It doesn't keep trying to start it up). I never experienced it but since a few users here confirmed the same, I tend to believe it.
    My question was never "how it feels when she tries to start up".

    Her beeps at me 150 miles before she actually runs out of fuel is really not very satisfactory to me. If you want to look at it from that way, then we can all assume that she will drive 500 miles when we fill it up and we would never need a gas gauge I guess. But nevertheless this isn't related to my discussion either. No Warning when the car really runs out of fuel is weird to me.

    And as for my follow-up question, Yes I think the "lack of fuel pressure" is the best bet so far.

    These all are my curiosity. I am not trying to run out of fuel. Just trying to get to know the car better.
     
  18. iskoos

    iskoos Active Member

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    I read Bob Wilson's thread but I probably missed this part. If the car shuts itself down to prevent the HV battery, it is a good thing to me. But I guess this was what Bob didn't like:). We all are different.

    Thank you for making this point. I will read Bob's thread again.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    Bob's complaint was that, while his Gen1 gave prompt dashboard warning that the ICE had quit running (quit burning fuel), Gen3 did not. Gen1 warned while there was still adequate traction battery charge to find safe pullout or parking. Gen3 silently switched to EV, giving no notice until the traction battery was depleted and the car became a glider. A conscious design step backward.

    I don't recall him complaining about protecting the traction battery, so you'll have to reread to check out that angle.
     
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  20. MelonPrius

    MelonPrius Senior Member

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    When my Prius shut off the ICE, there was a dashboard warning light, which I didn't recognize.

    I remember reading that after running out of gas, you might need to put in more than a gallon to get the car running again. Out of curiosity, after pumping one gallon of gas, I tried starting the car. It successfully started with no issues.
     
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