12volt battery/jump starting issues, help!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by AnnaBD, Jun 14, 2020.

  1. AnnaBD

    AnnaBD New Member

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    Hi. So I will state up front I am really not well versed in the auto world but am trying to learn as best I can.

    Today, my 2008 prius's 12volt battery had quite a day. A customer at my work (also in a prius) asked for a jump, I obliged, we each attached the cables under the engines of our respective cars and the jump worked great.

    Not long after, another costumer (in a Honda Pilot) needed a jump! I was feeling like the good samaritan and so I drove my prius over to her car (no problems) and turned it off. She pointed out the battery to me, which was positioned very oddly. I assumed she knew what she was talking about, and attached the cables where she directed as best I could, even though the whole setup seemed odd. There were two exposed connection points, and one of the was painted red and I assumed it was positive, and then I placed the ground on the other. There was a small spark, but not out of the ordinary (I think??). I went to try to turn on my prius to start the jump, and it wouldn't start at all. All dark.

    I immediately took off all the cables and went to grab a friend (with his truck). After looking at her owner's manual, we all realized that her battery was actually much more complicated than we thought and required removing a bunch of engine stuff to fully access. Plus, she had pointed out the terminal to me incorrectly. In the end, it seems like I definitely put the grounding cable on the Pilot's positive terminal, but that I had put the positive cable on a second positive terminal next to the primary one? Very weird? Does this count as reverse polarity?

    After that, my friend's truck successfully jumped both me and her (after much finagling in the Pilot's engine).

    I was able to drive home (about 10 minutes) but forgot that I should probably keep my car running and turned it off. So, I tried to start again, and it did not work. I was worried that I just hadn't driven it long enough, so I successfully got a jump from my landlord and drove it for much longer (about an hour) with no problems. When i got home, though, it wouldn't start again.

    I tried to look and see if any fuses were burnt and it didn't seem like it, but I wasn't sure of which fuses to check (the diagram in my manual was very confusing).

    What is the most likely prognosis? Was two jumps in a few hours too much? Did I just drain my battery? Destroy the battery? Fry a fuse or something bigger? If something in the electronics got busted from the reverse polarity, would my car still start when jumped (as it has twice)?

    I'm trying to see if I can borrow a voltage reader and trickle charger before I just go and replace the battery. Would love any and all suggestions!
     
  2. JC91006

    JC91006 Senior Member

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    From the internet

    Can you give a jumpstart with a Prius?
    The Prius does have 12V battery connections under the hood. ... These hood connections can be used to start the Prius or to trickle charge another car battery, but cannot be used to jump start another car (supplying power another car as it tries to turn the engine with the starter motor).
     
  3. AnnaBD

    AnnaBD New Member

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    Yeah, doing research now, I saw that. I could have sworn I'd jumped someone from my prius before, but perhaps I'm misremembering. And I did successfully jump the other prius earlier in the day. But maybe that only worked because it was another prius?
     
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    That's a pretty big "whoops". Unless you are intimately familiar with the Prius electrical system, it would be best to never, ever use your Prius to jump start any other car. The 12v system is not designed to withstand the electrical load created when starting a normal car, and in addition, any accidental reversing of leads is going to leave you stranded with a several hundred dollar towing/repair fee.

    Most often, reversing connections while jumpstarting a Gen 2 Prius results in blowing the main fusible link and 2 or 3 fuses in the engine compartment fuse box.

    Reading your sequence of connections and considering your car still functions when jumped, I would first look to see if you popped the main (120) amp fuse that is inside the housing of the 12v battery positive terminal connector.

    I made a photo sequence several months ago, included below, to help a fellow member do some troubleshooting. It should help you locate and check/replace the 120 amp fuse if needed. The 12v battery is located in the trunk, on the passenger side. Access will require removing the trunk storage bin.

    If you end up replacing the 120 amp fuse, make darn sure you tighten the 2 threaded fasteners that lock it in place, otherwise you're going to experience a lot of 12v gremlins.

    bat1.JPG bat2.JPG bat3.JPG bat4.JPG bat5.JPG bat6.JPG bat7.JPG bat8.JPG
     
    #4 TMR-JWAP, Jun 14, 2020
    Last edited: Jun 14, 2020
  5. ChapmanF

    ChapmanF Senior Member

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    If that's what happened, it doesn't count as reverse polarity, only as a short circuit. It likely blew one or more of the fusible links in the car (TMR-JWAP's post above shows where one of them is, in the battery clamp). Other than that, it probably did less damage than people see with actual reversed polarity.
     
  6. AnnaBD

    AnnaBD New Member

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    Yeah, I've learned that now! It was a crazy day and I was not thinking straight. Not something I will attempt again. Thanks for setting me straight.

    I'm going to go get my buddy's volt meter now and will see how the battery and that main fuse are reading. Thanks so much for the detailed photos!
     
    #6 AnnaBD, Jun 14, 2020
    Last edited: Jun 14, 2020
  7. Johog

    Johog Junior Member

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    The other replies make sense. The fuse at the 12 volt battery is my best guess.. with the engine off and nothing attached to the car.. see if the dome light comes on at all. Any light at all means that fuse is ok. Best answer then is to test each fuse. Invest in a cheap multi meter and watch YouTube for how to test fuses in the fuse box. You should be able to find a cheap meter for less than $20.

    you seem to be surrounded by folks that have car troubles. Spend $50-100 and get yourself a 12 volt jump pack. Just keep it in your trunk. That way you can be the good friend without risking your prius's very delicate 12 volt system.
     
  8. AnnaBD

    AnnaBD New Member

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    Okay, so I've checked the battery itself and its pretty consistently reading 12.5 volts or so. Using TMR-JWAP's instructions, I tested the voltage through the spot where the cable enters that main 120A fuse relay above the battery and still got 12.5 volts.

    But, when testing the power in the engine compartment, on the jump starting spot, I was not reading anything on the meter. Can I assume the issue is somewhere on the connection between the battery in the back and the connection up at the front? It does make me think - at one point in all the shenanigans yesterday, a friend did try to jump me from the back (because of the way I had parked) and it didn't work, but I've been jumped twice now up front and that got the car started just fine.

    As to Johog's question - I've got no light at all in the dome. No beeping noise if i leave the key in the ignition slot. No response at all from the car unless its jumped up front and then it functions normally until its turned off again. I've used the volt meter to test the smaller fuses in the engine and they all seem to be unbroken.
     
  9. dolj

    dolj Senior Member

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    Remove and actually check the 120 A fuse in the back with your ohmmeter. Unless you actually blew the wire between the battery in the back to the jump point in the front apart, it has to be that fuse.
     
  10. ChapmanF

    ChapmanF Senior Member

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    Don't overlook the similar 100 A fuse link that's bolted into the fuse box up front.

    When that one is opened, it leads to strange "partitioned Prius" situations because there are different circuits in the car that tap from each side of it. You end up with a car that stays on as soon as you can turn it on, but won't charge the battery, and you can't turn it on with only battery power from the back. Sound familiar?

    When you look at the wiring diagram, the fuse that powers the dome light is fed from the battery side of that link, so a meter would probably show you battery power at that fuse. Nevertheless, the dome light won't come on, because that's controlled by the Body ECU, which gets its power from ... the converter side of that link.
     
  11. AnnaBD

    AnnaBD New Member

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    whoops again. I got a better look at it this morning and yes, that 120A fuse is definitely blown. I don't know how I was getting any voltage reading through it yesterday, cause today I'm definitely not. I think I've bought the right replacement fuse and will try to fix it after work today. Any words of advice?
     
  12. TMR-JWAP

    TMR-JWAP Senior Member

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    Be careful unplugging the small white wire from the assembly. Many people have broken the wire off.

    If I remember correctly, the fuse is held in place by a 10mm headed screw and an 8mm headed screw. As mentioned previously, when installing the new fuse, fasten them securely or you'll have problems down the road.

    Remember, the battery terminal is tapered, it gets thicker as it gets closer to the battery body. Prior to installing the assembly back onto the battery, spread the clamp slightly to ensure you can push it all the way down onto the positive terminal. Then tighten the 10mm bolt on the clamp. I've seen several 12 v problems caused by the clamp being too far up the terminal and not tightening securely.

    Other than that, I think you'll handle it just fine.
     
  13. AnnaBD

    AnnaBD New Member

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    Thank you all for all your guidance! Yesterday I was able to replace the fuse and get the prius back up and running. Those pictures were absolutely crucial, TMR-JWAP. You're a prince among men!
     
    GrGramps and dolj like this.
  14. TMR-JWAP

    TMR-JWAP Senior Member

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    Glad to hear it all worked out well. (y)
     
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