2015 Prius Gen 3 not started for 11 months

Discussion in 'Gen 3 Prius Main Forum' started by Teja Reddy, Apr 19, 2021.

  1. Teja Reddy

    Teja Reddy New Member

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    I was out of town for a long time and left my car at a friend's place who was going to use it once in a while and apparently due to some unforeseen circumstances he had to go out of the country and so my Prius was left with not being started in close to 11 months now.

    I tried to jump the battery yesterday and was able to start the car but it would go off again as soon as i remove the jumper cable connecting to the other car and so in the 2nd try i kept on pushing the throttle while my friend removed the jumper cable connection, the car remained on but i got an error stating that the key was not detected, while i had it inside the car ? does it mean that the key fob is out of charge or is there something else going on ?

    I am relatively new to hybrid cars (only used it for 5-6 months before going out of town) so appreciate any suggestions/info on this.
     
  2. PriusCamper

    PriusCamper Senior Member

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    Hook the 12v battery up to a legit battery charger overnight and try again...
     
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  3. bisco

    bisco cookie crumbler

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    buy a new 12v. if the fob lites up, it is working. 'key not detected' is a misnomer
     
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  4. Teja Reddy

    Teja Reddy New Member

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    Thank you, will try that, I'm also thinking that the battery in the key fob must have also died as i don't see any light coming from me pressing any buttons on it.

    Thank you will try charging it up but if it doesn;t work then I'll probably buy a new 12v battery, based on both the replies I am now less worried that the Hybrid Battery might be completely dead, I'm also thinking that the battery in the key fob must have also died as i don't see any light coming from me pressing any buttons on it.
     
    #4 Teja Reddy, Apr 19, 2021
    Last edited by a moderator: Apr 19, 2021
  5. Mdv55

    Mdv55 Active Member

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    You need a new, or if you're lucky, better charged 12V battery.

    The Prius doesn't charge the aux battery very well like a normal car does so revving the motor does nothing for you. It's dying because once you remove the jumper cables the 12v in the car can't support itself and the car freaks out and shuts down. The Prius "charging" system for the 12V is more like an old school trickle charger and not something that slams a lot of amps to that circuit. If the 12v battery is dead enough the car can't recover it. You might get lucky and a real battery charger will bring it back to life enough but after 11 months it's most likely just toast unless it was pretty new to begin with.

    Don't chase any other symptoms until you start with a known good 12v battery in there.
     
  6. Grit

    Grit Senior Member

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    but I heard the hv battery takes over once 12v hands it over.
     
  7. Mdv55

    Mdv55 Active Member

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    If the HV system takes over for the 12v battery why do we get weird errors when the12v battery is old then?If the HV system takes over for the 12v battery why do we get weird errors when the12v battery is old then?

    The 12v battery is part of the system and everything is electronically controlled/regulated to certain parameters. If the 12v is dead enough the parameters the computers want to see aren't possible and the chain is broken so to speak. That's when flaky things happen. I'm not an expert, but these cars seem crazy voltage sensitive and act weird when things aren't in line. Again, reference when the 12v is old and starts to go. If the car was entirely dependent on the HV system to supply the 12v system we wouldn't have those issues. It would either work or it wouldn't.
     
  8. ChapmanF

    ChapmanF Senior Member

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    I see this getting said now and then, but it's a picture that doesn't match how the car is built.

    There is no "charging system" for the 12 volt battery; there is simply the car's 12 volt electrical system, which the battery is directly attached to, as well as the DC/DC converter that supplies that whole system with power when the car is READY.

    The output of the DC/DC converter in Gen 3 is generally between 13.5 and 14.8 volts, and that is the voltage that arrives at the battery. The converter is rated for a maximum output of 120 amps, and there are only two fuses between it and the battery: the 125 amp "DC/DC" fuse in the front fuse box, and the 140 amp "MAIN" fuse at the positive battery clamp.

    [​IMG]

    [​IMG]

    There isn't anything in the circuit that specifically limits what current will go into the battery. Nothing there but fat copper wires. Whatever current the battery will accept, in its current state of charge, at the voltage the DC/DC converter is supplying to the car, is the current that flows into the battery.

    Now, the part of the story that has the kernel of truth is that, usually, the converter's output voltage range of 13.5 to 14.8 volts does not result in the battery accepting a super high current.
     
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  9. AW82

    AW82 Member

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    Did you disconnect as soon as you saw the "ready" light? Or did you at least wait for the ICE to kick on? I wonder if the HV also being depleted is a factor.

    Related to the above, do spark plugs, fuel pump, etc. all run on 12v?
     
  10. rjparker

    rjparker Senior Member

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    A completely discharged and failed 12v battery can be a serious current sink to any source. Best to get a new one in there and try again.
     
  11. Mdv55

    Mdv55 Active Member

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    What controls the power that goes to the converter in the first place? There has to be something else going on in the background that is complicating things when the 12v battery gets flaky. I keep seeing tons of admonishments to limit charging current to the 12v battery so it doesn't get damaged so something must regulate it. Or are you saying since resistance is fixed and the only other variable is the tight voltage range that keeps current in check automatically?
     
  12. ChapmanF

    ChapmanF Senior Member

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    Yep, everything in the car except for the hybrid powertrain itself and the compressor for the A/C.

    I think in some trims (the ones where the power steering motor is brushless, which I think are the ones that came with 17" wheels), that motor may be fed a somewhat higher voltage, but just boost-converted from the 12 volt system still.
     
  13. royrose

    royrose Senior Member

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    I left my 2010 when it was 4 years old with a friend for a year while I worked abroad. The friend was supposed to drive it once in a while but hardly ever did. (Maybe we have the same friend). The 12v battery was dead. I didn't try to jump start it, just replaced it. The new 12v and the original hybrid battery have worked perfectly since.

    Since your 12v battery is 6 years old and has been stressed by sitting, I think it is best for you to replace it and get long life going forward.
     
  14. ChapmanF

    ChapmanF Senior Member

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    Well, the behavior of a lead-acid battery at different charge states is a much longer story than "resistance is fixed". The converter's output voltage range, around 13.5 to 14.8, is not really what I would call 'tight'; the amount of current a battery is going to accept at 14.8 will be higher than at 13.5, and more than just linearly so.

    I think what's happening in a lot of people's heads is they're seeing the label on the battery warning that "when you charge battery, charging current should not be higher than 4.2 amps", and they assume there must be something in the car that also keeps the car's charging current under that limit, but there just isn't. If you put an ammeter there you can see higher charge currents flow. They usually decline fairly quickly as the battery charge comes up, and end up being around that label-suggested ballpark most of the time. That's as close as the car bothers to hit the target. I think the label on the battery mostly translates to "please do not hook to your wheel-around 50 amp fast charger, thank you."
     
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