Elerctrical Issues After Battery Reverse Polarity Connection

Discussion in 'Gen 2 Prius Main Forum' started by PriuSocal, Mar 10, 2025 at 12:14 AM.

  1. PriuSocal

    PriuSocal Junior Member

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    Posting this for a friend who just called me with this issue.

    He is not mechanically inclined and went to replace the 12v battery on his 2005 Gen 2 and he mixed up the polarities and hooked up + to - and vice versa and he said the car lights started to go on and off as well as the horn and he immediately disconnected the battery and reconnected it back correctly but said the car will no longer turn on now after the event.

    I personally thought nothing would happen other than a big spark or fried wiring if connecting your battery cables incorrectly but it has never happen to me so IDK. Anyhow, I am hoping this prius has some sort of fuse that would pop to prevent further damage to the electrical system on the car and assume its on the positive cable under the red top or not? I would like to know what to look for before going to him and trying to assist him.

    Any help would be greatly appreciated by my buddy Ron :)
     
    #1 PriuSocal, Mar 10, 2025 at 12:14 AM
  2. dolj

    dolj Senior Member

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    Search the Gen 2 forums for reverse polarity jump. There are a lot of threads on this and what needs to be done to repair the damage.
     
    #2 dolj, Mar 10, 2025 at 4:52 AM
  3. Hayslayer

    Hayslayer Member

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    There are 2 (or 3) fuses that likely blew in the under hood fuse box (i don't remember which ones, off the top of my head), plus the main fusible link in the fusible link assembly (the white plastic unit with the clear plastic top in the upper left corner of the fuse box).
     
    #3 Hayslayer, Mar 10, 2025 at 5:33 AM
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  4. ChapmanF

    ChapmanF Senior Member

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    Also don't forget to check the 5 amp one in the twofer fuse carrier on the 12-volt battery positive post.

    If that fuse is open, you will get DC/DC converter trouble codes, which have led some to be told they needed to replace the $$$ inverter assembly also.
     
    #4 ChapmanF, Mar 10, 2025 at 7:42 AM
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  5. Tombukt2

    Tombukt2 Senior Member

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    Doesn't this usually take out the fusible link the clear thing takes up about five spaces and the fuse box That's a real pain in the butt but I think that's a thing along with all the other fuses discussed.
     
    #5 Tombukt2, Mar 10, 2025 at 10:59 AM
  6. rjparker

    rjparker Tu Humilde Sirviente

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    You can normally see the blown links. Replace as a module.

    Prius Gen2 Eng Fuse Box & Fusible Link Mechanical.jpeg Prius Gen2 Fusible Link w Tabs and Cable ID.jpeg
     
    #6 rjparker, Mar 10, 2025 at 11:44 AM
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  7. ChapmanF

    ChapmanF Senior Member

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    It was mentioned in post #3.
     
    #7 ChapmanF, Mar 10, 2025 at 2:16 PM
  8. Tombukt2

    Tombukt2 Senior Member

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    Oh I didn't even see it but I thought that usually takes part of this thing out and then you dissecting your fuse box.
     
    #8 Tombukt2, Mar 10, 2025 at 2:22 PM
  9. PriuSocal

    PriuSocal Junior Member

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    As mentioned, this was NOT a jump…this was a battery swap / replacement.
     
    #9 PriuSocal, Mar 10, 2025 at 3:53 PM
    Last edited: Mar 10, 2025 at 4:02 PM
  10. PriuSocal

    PriuSocal Junior Member

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    This is Gold, thank you very much for the detailed reply!

    @Tombukt2 Appreciate your input

    @ChapmanF Thank you for the input, He is inable to see any trouble codes as of yet as the car will not start up and nothing happens when attempting to hit the power switch. I will have to physically go to him to try and assist him and check out the fuses.

    @Hayslayer Watched all the videos showing the fusable link replacement but my 1st look at will be the fuse on the + cable of the battery. Then move on to the fuses under the dash and finally the fuses on the fusable link. Will something be very obvious if the fusable link goes bad? Like is there an actual fuse or bridge that pops on the link itself or? The videos I have seen shows the fusable link as just some sort of bridge that connects all the fuses together and to the car but did not see an actual fuse on the link itself or a point where they crack/sever or pop.
     
    #10 PriuSocal, Mar 10, 2025 at 4:00 PM
  11. ChapmanF

    ChapmanF Senior Member

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    The white fusible-link module is a single assembly serving as a bunch of different high-current fuses serving several different circuits. The big one at the top end is the 100 amp DC/DC fuse.

    The Toyota wiring schematics are kind of unhelpful in the way they just show those all as if they were separate fuses, and you kind of just have to know they're just different fusible connections inside that one white thing.

    It has a clear cover on top, so you can see which connections inside it have let go.

    Unless you have a used one that has been out in sunlight for months in a boneyard. Then the top isn't clear anymore. But the top also pops off fairly easily (you can see where the clips are), and then you can see which connections inside it have let go.
     
    #11 ChapmanF, Mar 10, 2025 at 5:02 PM
  12. dolj

    dolj Senior Member

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    Okay, it wasn't a "jump" but it was a reverse polarity connection. Apart from the semantics, it is the same result.
     
    #12 dolj, Mar 11, 2025 at 12:37 AM
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