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12v drain and P0aa6 code

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jesse Floyd, Feb 27, 2023.

  1. Jesse Floyd

    Jesse Floyd Junior Member

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    Hello all, I'm fairly new to PriusChat, I've been a lurker for awhile but never really posted anything.
    I have a 2005 Prius that I bought for 1k with a bad engine and battery pack. I used some cells I had lying around, refurbished the pack and replaced the engine. I used new nickel plated busbars and nuts for the connectors since the old ones were severely corroded. I replaced the 12v battery because I thought it was bad. Turns out, there is a massive drain on the 12v system and I'm completely unsure what it is. It seems that when the high voltage battery is unplugged from the car, the 12v stays fine and works beautifully. But when the high voltage battery is plugged in and the car is left overnight, the 12v drains to absolutely nothing. I also have the dreaded P0aa6 code with nothing but the 526 inf code. I am desperate to find out what is going on, any direction on things to try or where to look would be fantastic. I would be extremely grateful.
     
  2. bisco

    bisco cookie crumbler

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  3. rjparker

    rjparker Tu Humilde Sirviente

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    I would get rid of the hv battery isolation code first. 99% its something you did in your combined engine and hybrid battery swap.

    Most likely pulling the orange disconnect is a red herring unless its the battery ecu magically shutting down as a result. You may be waiting longer and normal computer shutdowns have finally happened. Even opening the door or hatch wakes up some computers. Or you have determined the battery isolation fault is in the hv battery assembly.

    Concerning the possible parasitic draw: Measure the parasitic draw after waiting about 15 minutes for everything to shutdown. Then the brute force diagnostic is to pull one fuse at a time while watching the amp draw after taking a very good picture of the fusebox to ensure you return the right fuse to the right slot. Include the engine and interior fuse boxes. After you find the offending fuse, get a circuit diagram and determine what that fuse feeds. It can be anything but its often aftermarket additions or something plugged into the obd2 port. Be careful, many try this and end up making things worse by reinstalling the fuses in wrong slots.

    There are more advanced methods to locate a parasitic draw such as using a thermal imager to look for heat buildup and millivolt analysis of in circuit fuse voltage drops. But the first thing is to ensure the draw is really there after a shutdown time period.
     
    #3 rjparker, Feb 27, 2023
    Last edited: Feb 27, 2023
  4. ChapmanF

    ChapmanF Senior Member

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    Just so we're not guessing, what do you mean by "when the high voltage battery is unplugged from the car" and "when the high voltage battery is plugged in"?