HV hybrid traction battery blues

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Carmen TheWonderDog, Oct 18, 2025 at 10:34 AM.

  1. Carmen TheWonderDog

    Carmen TheWonderDog Junior Member

    Joined:
    May 31, 2024
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    Location:
    Central IL
    Vehicle:
    2008 Prius
    Model:
    Base
    My ‘08 Prius* isn’t behaving nicely AFTER I (think I?) just hooked up a newly ordered reconditioned battery to replace original, as it had been inoperable & throwing hybrid battery codes (forgot to ask which, duh!)

    What could be going on? How do I troubleshoot from here?

    Bad behavior = Electrical comes on, no engine. I had a code reader on, but all I saw was a lot of data & no codes. Upon trying to turn car off, it won’t shut down per se, dash remains ablaze w/ various odds & ends lights, but nothing functional. Eventually, lights out.

    A. Could 12V discharge have caused this? Though I don’t think it was, having been unhooked from the HV. Also, when I popped the charger on it, it was at low 12 something V & very shortly after @ 14ish V. Fully charged now.

    B Did I break the refurbished battery? Didn’t have all correct sockets/adaptors to tighten screws to spec (helpful neighbor friend only watched video & dopey me didn’t read through entire protocol before point of no return‍♀️) so just hand tightened w/ not particularly strong arms.

    C. I can reverse the installation & carefully repeat to spec, now that parts have arrived.

    * low mileage (~130-150kmi?), brutal summers, freezing winters, short trips.

    Blaze of warning lights while on highway otw home, including red triangle of doom, soon inoperable (barely got to help).


    much TL:DR!
    My trusty low-ish mileage (120-150kmi? IDK, don’t drive much or far) ‘08 became inoperable several weeks ago after a blaze of warning lights (including the red triangle of doom) while otw home, pulled over highway, no phone!, hazards, limped along to get to help, made it to a house, then it truly gave up the ghost & refused to move as I tried to relocate it to a less inconvenient spot for the homeowners. Juice, but not engine turnover.

    My mechanic said it was throwing hybrid battery codes. Dope that I am, I failed to ask & record which ‍♀️.

    Having no hybrid battery techs in town, I opted to order a refurbished unit & attempt the swap w/ my neighbor’s assistance; bit of a gamble for a complete novice but quite intelligent & a good problem solver + a master carpenter who once went to motorcycle repair school.

    Short story long, neighbor completed disassembly (save battery pack itself) solo, in my absence. I picked up w/ opening battery pack once refurbished cells unit arrived.

    Hit a couple few road bumps:

    1) one bus bar screw hole in refurbished unit isn’t patent, something shiny silver metallic in the way, vendor says DON’T need ANY bus bar screws!?! By now I’ve removed & replaced these 28 screws around a half dozen times, by hand, we’re old friends & my hand is sore. I stick the darn things in anyhow.

    2) Am caught off guard with the specs on screw tightening; of course one should read through the ENTIRE procedure before deciding to take it on (duh…), but I was preoccupied w/ a broken tooth & violent neighbor-tenant & resulting court so I trusted best friend neighbor who said it was doable (here, somewhere in the recesses of my brain was a niggling feeling - He likes to watch videos to learn things, while I LOATHE them because they take too much time, are inconvenient to go check just one step, and aren’t text!). Well, I expect there wasn’t any mention of in/lbs or ft/lbs in the video, b/c neighbor didn’t have the tools.

    : find right torque wrenches, borrow them, realize need adapter for quarter inch wrench or 1/4” sockets, wrong adapter arrives…) Impatience sets in before correct sockets/adapter on hand & I just hand tighten to my weakling standard, thinking I just want to see if it works.

    3) Neighbor not feeling cooperative for reassembly assist, so I just follow written/pictorial steps. Only a few missing & extra parts; nuts, bolts & plastic bits not seen in pix (non-essential?)
     
  2. xw20_driver

    xw20_driver Junior Member

    Joined:
    Feb 4, 2025
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    Location:
    PNW
    Vehicle:
    2007 Prius
    Model:
    Touring
    Was the refurbished HV pack completely intact with ECU, relays, and components or did it only consist of the 28 blades and you had to transfer your existing ECU and components onto it? What is the resting voltage of your 12V battery? If you still display the red triangle you can pull the codes.
     
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
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    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base