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Alarm randomly went off and car won't start now

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PriusFruit, Jun 7, 2021.

  1. PriusFruit

    PriusFruit Member

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    So this happened to me last month - Prius alarm randomly went off in the middle of the day and then I went to start the car and it didn't start. After some research I found out it probably was an issue with the 12V battery.

    Bought a new 12V battery from Toyota and went ahead and replaced it. Everything was good until today.

    Same thing happened about half n hour ago. Alarm randomly went off and when I went to start it the dash turned on, made some beeping sounds and then it powered off.

    I only tried to start it once, because last time I kept trying and it killed the battery even faster. I'm not sure what else it can be now.

    Any ideas on what could be causing this?

    I replaced the 12V last month and the hybrid battery in 2020, so I'm not sure what else it could be.

    Only other thing is the weather is hot here and I usually crack the windows to not let it overheat too much in the car, but then again today isn't a record hot day here.

    Thanks!
     
  2. JC91006

    JC91006 Senior Member

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    check your 12v voltage. If it's low again, then it's probably draining on it's own. Often aftermarket alarms will cause these issues when they age.
     
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  3. rjparker

    rjparker Tu Humilde Sirviente

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    Is it an aftermarket alarm?
    -Some aftermarket alarms are sensitive to voltage.

    Have you checked the 12v voltage now?
    -It could be low again.

    Did anyone measure the parasitic draw?
    -Excessive off state current draw, usually over 30ma can drain a battery.
     
  4. PriusFruit

    PriusFruit Member

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    Luckily I just found this thread - Prius won't start. No lights come on except a little lock symbol. | PriusChat

    And it mentioned trying out another fob. I went ahead and tried my second fob key, inserted into the slot, and the car started no problems.

    Do you think my original key fob is low on batteries and triggered a panic alarm?

    -

    edit: I started the car a few times and it looks to be okay. Changed gears and things worked. It might be a little premature to say everything is fixed now though.

    edit #2 - @JC91006 I don't have the tools to check that. I also bought the car used, so I don't know for sure if it's an aftermarket alarm. I wouldn't think so though. I've had the car for about 4 years and no problems with the alarm before. Also it sounds like a Toyota alarm.

    @rjparker I'm not sure about the parastic draw. Do you need a voltmeter to check that?
     
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  5. rjparker

    rjparker Tu Humilde Sirviente

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    Parasitic draw can be checked with a voltmeter but it involves removing a battery wire. Repairing a problem when found is more advanced. However a different fob starting it makes 12v issues far less likely.
     
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  6. PriusFruit

    PriusFruit Member

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    Thankfully it got me home today with no issues after it happened. I'll see how it drives the rest of the week and give an update. Still strange the key fob had something to do with this (possibly).
     
  7. TMR-JWAP

    TMR-JWAP Senior Member

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    The gen 2 will typically beep at you when the FOB battery is getting weak. have you noticed any little beeps from the interior of the car when you weren't expecting it?
     
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  8. PriusFruit

    PriusFruit Member

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    @TMR-JWAP I haven't noticed any beeps. I do remember hearing that sound a couple years ago and finding out from here that it was because the fob battery was dying.

    Drove the Prius again today and no issues with the new fob.

    12V battery is new and hybrid battery is new. So if it happens again maybe it's an electrical problem, something with the alarm or a faulty 12V, but I doubt it's that.
     
  9. pasadena_commut

    pasadena_commut Senior Member

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    Or get a clamp on DC ammeter - MUCH easier to work with. Just be aware that all the really inexpensive clamp on ammeters are AC current only.

    I have a UNI-T UT210 which showed that just opening a door (or the hatch) with the car off resulted in 500 milliamps of current from the battery, whereas with everything closed it was only 15 mA. Measured right at the cable coming off the battery.
     
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  10. PriusFruit

    PriusFruit Member

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    Update: Sunday, June 13th

    Thankfully things have been back to normal since I posted this. The alarm hasn't gone off again and the car's running beautifully. I ended up changing the fob key with a new replacement I bought a while ago.

    Thanks for the advice everyone.
     
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