Dose this sound like an alternator issue or the 12V?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by james1977, Nov 27, 2021.

  1. james1977

    james1977 New Member

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    I have a 2011 Prius with 140K miles.

    The car has been starting slow for the past few months. Sometimes the locks were also weak to open.

    This morning - our first truly cold one in a while - the car would not start. I got a bunch of warning lights on the dashboard. With continued presses of the power button, it seemed like the 12V died completely. No warning lights on the dash anymore and the locks will not open.

    The hybrid battery seems okay. The car shows that it is usually fully charged during drives. It was 80% charged when I got the slew of warning lights this morning.

    I tried to jump the car but it will not jump start. It could just be that the portable jump starter is not fully charged. It was sitting in the trunk for a few years without one. I am charging it now.

    I have a check engine light and, under the hood, I hear mad buzzing from the alternator.

    If it is just the 12V, this would be the third in four years. Does it make sense that the 12V batteries would keep going bad during such a short time frame? Or could this be a problem with the alternator? Like I said, even though the car will not start, it is making a lot of noise.
     
    #1 james1977, Nov 27, 2021
  2. bisco

    bisco cookie crumbler

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    either possibility. if you don't drive much, you're just killing the 12v, and you need a battery tender.

    otherwise, you will have to measure the quiescent draw on the battery when the car is off, and compare it to the spec from the repair manual.

    an easier way might be to disconnect the 12v and see if it drops overnight.
     
    #2 bisco, Nov 27, 2021
  3. ASRDogman

    ASRDogman Senior Member

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    You keep mentioning the "alternator". The Prius doesn't have an alternator.
    How often do you drive the car, and for how long? If you don't drive much or often,
    you should get a battery tender, as mentioned.

    You should also check to make sure you are not leaving anything on. Turn off all accesories
    before shutting the car off.

    The buzzing is not the alternator, because the Prius doesn't have one. It's more likely that it
    is the brake actuator trying to build up pressure with a low 12v battery.

    Hopefully you can get the car started after charging your jumper.

     
    #3 ASRDogman, Nov 27, 2021
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  4. jerrymildred

    jerrymildred Senior Member

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    Welcome @james1977.

    This^^^

    This, too. ^^^

    Oh! And this as well. ^^^

    The long buzz from the brake actuator is a great clue that you have a low 12V battery. Since your battery relatively new, it's most likely getting run down by short trips.

    As mentioned, you do not have an alternator. But you do have a DC/DC converter that charges the 12V battery. It's part of the inverter. Hyper-easy to check it. Just put a volt meter on your battery terminals or on the jumper points under the hood. With the car in READY, it should read about 14 volts, or at least well over 13. Those converters very rarely fail, but it's easy to check.
     
    #4 jerrymildred, Nov 28, 2021
    Last edited: Nov 28, 2021
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  5. james1977

    james1977 New Member

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    Thanks for the replies. It was the 12V. I replaced it back in November and haven't had a problem since.
     
    #5 james1977, Mar 21, 2022
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    #6 mr_guy_mann, Mar 22, 2022
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    How often are you driving, and how long are your trips? If your usage is low/sporadic, you may have problems with the new battery soon.

    Also, what's your "parking situation", ie: private garage with AC outlets, underground parking with/without AC outlets, carport with/without AC outlets, or street? If your usage is low, and it works for you, an appropriate smart charger will protect the battery from running down.
     
    #7 Mendel Leisk, Mar 22, 2022
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