Not starting....then starting!

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by richbaxter, Dec 18, 2019.

  1. richbaxter

    richbaxter Junior Member

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    Hi all
    I have a Gen 3 Prius. Its been bullet proof for the 2 years I've had it so far. Just recently, I've got in (always at night when colder) and press the start button. Only the top display of the dash lights up and the radio/sat nav and climate control doesn't light up at all. I can't put it into gear. It takes a few tries to turn it off with the start button sometimes going from green to orange before turning off. Often I have just gone out, locked the car, unlocked it and got back in and it starts. Other times like last night, it took me 10 mins to get it to turn on properly and start. Same every time though, top dashboard display lights up, radio and climate control doesn't until it decides to start. I thought it maybe my key fob battery so I changed that and for 2 weeks, it was fine but it did it again last night. If its the 12v battery, wouldn't it show up on my dashboard with a warning and also if it was the 12v battery, surely once its low enough not to start the car, then I wouldn't get it started at all? But it does eventually start and drives fine without any warning signs. Thats the bit I find confusing.

    Any advice would be great

    Thanks!
     
  2. FrankB

    FrankB Member

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    Definitely check your 12V as you will not get a warning to change it. All the 12V does is boot the computer enough to allow the high voltage battery to take over which then starts the car.
     
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  3. richbaxter

    richbaxter Junior Member

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    Thanks Frank, I will do that. I guess i have to get used to how it starts the car over a conventional 12v battery as the fact I can start it eventually is the bit I've found a head scratcher! If it stops bloody raining, I'll charge it up without removing it as I've disconnected it before and that alarm went mental and blew my head off!
     
  4. Rebound

    Rebound Senior Member

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    Most likely cause is the 12V battery. You can prove by using a jump pack or jumper cables but that will just prove you need a new battery. Many auto parts stores will replace in the parking lot for free.
     
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  5. sam spade 2

    sam spade 2 Senior Member

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    You are not alone with being confused by this kind of behavior.

    NO, there is no "low battery" warning because it would have to be produced by a computer board and THAT is what is not booting up right to allow it to start.
    It is not unusual for repeated attempts at "booting" the computers to finally get far enough to actually run.

    Get a new 12 V battery......and/or check the main battery connections.

    Note: Charging is only a bandaid. Might only help for one trip or a few days.
     
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  6. richbaxter

    richbaxter Junior Member

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    Running a vehicle check it shows on the screen the battery is 14.1v charged so it can't be that surely?
     
  7. richbaxter

    richbaxter Junior Member

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    It just turned over fine first time...
     
  8. jerrymildred

    jerrymildred Senior Member

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    All this does is show how many volts the charging system is putting into the battery. It's like checking the voltage on a battery in a conventional car while the engine is running. It doesn't say much about the battery itself. For that, you need to shut off the car, let the battery rest a few hours, and then check it with a multi meter.
     
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  9. Rebound

    Rebound Senior Member

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    Prius doesn’t run a starter from the 12V battery, like normal cars.

    The 12V battery powers electronics and closes relays which engage the high voltage traction battery. It is this battery which starts the engine. That’s why the Prius can start up strong even with a marginal 12V battery.
     
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  10. sam spade 2

    sam spade 2 Senior Member

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    That is NOT the battery voltage but the voltage of the battery CHARGING SYSTEM.
    That proves nothing about the battery itself.
     
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  11. richbaxter

    richbaxter Junior Member

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    Even if the engine isn't running after a cold start for nearly 20 hours? (I put it in Eco mode to stop the engine from running during the check so the engine hadn't fired up by then). I get its pointing at a new battery but I'm just not getting this "start fine for 2 weeks then a few days of trouble, then fine again" routine, plus why it gave that reading of 14.1v when the engine hadn't fired up for 20 hours. Just want to be sure.
     
  12. bisco

    bisco cookie crumbler

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    the engine doesn't charge the 12v, the hybrid battery charges it through the inverter.

    there's no altenator, the engine charges the hybrid battery through the tranny generator and inverter.

    you can do a 12v check without the car 'ready', which would show the battery charge minus whatever electronics are powered up
     
  13. jerrymildred

    jerrymildred Senior Member

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    What @bisco said. (y) The engine has nothing to do with charging the 12V battery. If the car is "READY" it's maintaining the aux battery voltage. Always.
     
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  14. richbaxter

    richbaxter Junior Member

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    OK, cheers guys! I'll have to wait until after Xmas plus I hope a 300 mile round trip on Monday will help keep it flowing until then.
     
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  15. sam spade 2

    sam spade 2 Senior Member

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    You still aren't thinking in the "hybrid mode". ;)

    The "system" is running even if the gas engine is NOT.
    That includes the "inverter" that charges the 12 V battery from the HV hybrid battery.
    The gas engine does NOT have to be running to do that.
    Any time the system is in READY mode (running) the inverter produces about 14 V, independent of what the gas engine is doing.

    I tried to explain why it works sometimes and not others.
    Summary: For the system to start (not the gas engine), several computer boards must boot up completely and properly.
    If the 12 V battery voltage is marginal, sometimes they will boot OK and other times not. The exact reason isn't important.
     
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  16. sam spade 2

    sam spade 2 Senior Member

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    Good luck.
    You likely will need it.
    I hope it doesn't fail at the "outer end" of your trip.
    Once in this condition, no amount of charging will make it "well" again.
     
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  17. richbaxter

    richbaxter Junior Member

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    Thanks guys, I appreciate the help and understanding!
     
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  18. bisco

    bisco cookie crumbler

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    pleasure!
     
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