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2004 Prius 12 Volt Battery Questions/Troubleshooting

Discussion in 'Gen 2 Prius Main Forum' started by Shmeckledorf, Jan 5, 2019.

  1. Shmeckledorf

    Shmeckledorf Junior Member

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    I have a few questions about my 2004 Prius and its 12 Volt Battery, but first here is some context to help everyone understand the situation.

    Yesterday afternoon I turned on my Prius and found that only the dashboard would come on. Among other things, it showed the warning triangle, the check engine light, and that one of my doors was open (although everything was closed). I tried to reboot it, which caused everything to die. The only thing that will turn on now is the check engine light.

    My hypothesis: My trunk is broken so it can't be opened from the inside or the outside. Occasionally it will come loose and the car will consider it to be opened. Usually all I have to do is push it back into place to fix that. In fact, the last time I used my car, I had to do exactly that. That was about 3 days ago. I'm guessing that the trunk became loose again and drained the car's 12 volt battery.

    What I Know or Have Already Tried:
    1.
    The main battery must be fine. I replaced it about a year and a half ago. I don't know if the 12 Volt has ever been replaced.
    2. Everything is connected. I checked the connections to the 12 volt and the main battery.
    3. When I try to turn on my car, a soft and steady clicking noise can be heard coming from beneath the hood
    4. I tried jump-starting it. All of the electronics came on, but the engine still would not start. As soon as I disconnected the two cars, the Prius would immediately die again.
    5. After the car died, the key fob won't lock or unlock anything anymore.
    6. It has almost a full tank of gas, and it has appropriate oil levels.

    Questions:
    A. Would my 12 volt battery stop my engine from starting? I've searched online for hours and I can't get a clear answer, even on Prius chat. Some people say that you can drive the car even when the 12 volt is completely dead, and others say that it has to have some charge to start the car.

    B. How much should it cost to have it replaced and installed? Most of the posts I've found about this issue list outdated prices. From what I've found online, replacement batteries are roughly $250. I've called two Toyota Dealerships, and one listed the cost of replacing and installing it at $300, and the other at $350. Is that reasonable?

    C. If it isn't the 12 volt battery, what else could cause these issues? I've seen some posts saying that there could be something wrong with the accelerator or the starter, but they don't really elaborate on that. In the days leading up to my Prius dying, I didn't notice any issues. There weren't any noises, it accelerated normally, and the lights weren't dim.

    D. Is there a way for me to run my car long enough to get it to a dealership or an auto-shop? This is my first car, and it's hybrid, so no one in my family has clue on how to get this to work. I can't tell if the battery won't hold a charge at all, or if I didn't charge it long enough? Towing on top of the other expenses would be very difficult on my family right now.

    Thank you for your time and help!
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    You can drive the Prius once the car is made READY. The 12V battery can be disconnected after the car is READY. However you need a good 12V battery to make the Prius READY.
    For a Toyota dealer service department, those prices are reasonable. You've determined that a replacement battery costs $250 online. Is it worth $50 or $100 for you to figure out how to install the 12V battery yourself?

    Also, if you look further you can find a correct 12V battery at lower prices, for example $150 at amazon.com:


    How about right now? Turn on the headlights and see how bright they are. If they are dim, that is strong evidence that the 12V battery needs to be replaced.
    If you can figure out how to correctly jumpstart the car, you potentially could drive the car. However if you botch the jumpstart by incorrectly connecting the jump cables, you might destroy the inverter. So pay attention and make sure you connect positive to positive.
     
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  3. bisco

    bisco cookie crumbler

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    you will need to open the hatch to replace the 12v. if you can't, toyota will charge you more to open the hatch and/or fix it (which it really should be so you don't keep draining the battery) or even more to crawl in the back from the side door and do it from inside, which would be a pecker of a job.

    after you have a good 12v, if it still won't start, you will need to have the trouble codes read.
     
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  4. Skibob

    Skibob Senior Member

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    This statement is a little disturbing. Did the engine spin and try to start? Generally once the relays close the car uses the traction battery to run the car. If the engine spun and did not start you might need to clean the MAF and change the plugs to get the car back to a baseline condition. As the car drives the computer adjusts settings based on what the sensors say. When the 12v dies those changes get reset, sometimes so much the car won’t start. So did the engine try to start (spin) and not start?
     
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  5. JC91006

    JC91006 Senior Member

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    4. I tried jump-starting it. All of the electronics came on, but the engine still would not start. As soon as I disconnected the two cars, the Prius would immediately die again.

    I've encountered this problem before, it was the white plugs on the battery that's not snapped in tight. One of the plugs was loose and the battery would disconnect from the car the minute power was removed.
     
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  6. Shmeckledorf

    Shmeckledorf Junior Member

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    Yeah, it's pretty concerning. The engine did not spin at all. Far as I could tell, the engine wasn't getting any signal to start at all.

    I just went into the car and removed the 12 volt battery. All of the white plugs were in there very tight. Perhaps there is something wrong with the wiring?
     
    #6 Shmeckledorf, Jan 7, 2019
    Last edited by a moderator: Jan 7, 2019
  7. Shmeckledorf

    Shmeckledorf Junior Member

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    UPDATE: I removed the 12v battery and I took it to a nearby Autozone. Apparently it is only 2 years old, but it had only 3v in it. They are attempting to charge it now. I've read that these batteries should last for 5 years, so perhaps it's faulty? If it DOES charge, I'll attempt to reinstall it and hope that it will be enough to start the engine. Then I can get it to an auto shop.
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. If the battery is only 2 years old, is it covered by warranty?

    2. Assuming you get the car to start, why would you take it to a shop? Would that be to fix the hatch so it will stay locked?
     
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  9. caminoramon

    caminoramon New Member

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    My 12 v is dead, could i just buy a regular 12 v from walmart because the dealer locally is quoting $350? Is the 12v battery special? I mean could I just install a battery that fits from walmart?
     
  10. JC91006

    JC91006 Senior Member

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    The $350 is probably an installed price. The list price on the Prius battery should be less than $250.

    Many dealers have online pricing that they will match. Do a search online to see if there's online pricing for that specific dealership. Longo Toyota has a website that sells parts online for less than the parts counter price. Just have to ask them to match the online price.
     
  11. asjoseph

    asjoseph Samuel, '04 Ruthiemobile

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    ... I'm seriously lending thought, when next changing my 12v battery, going with the vented OEM Panasonic variant, from Toyota's Avalon hybrid. One of my dear colleagues ponied up for her 2015 hybrid Avalon, brand new. Seven years before she'd changed hers, her OEM Panasonic outlasted two of mine! - Samuel, '04 Ruthiemobile.
     
  12. bisco

    bisco cookie crumbler

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    fitment will be required