2004 gen2 won't charge hybrid battery on highway

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Glassmandave, Sep 23, 2025.

  1. Glassmandave

    Glassmandave New Member

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    Hi all, I hope someone can help--I'm near my wit's end with this.
    My 2004 has 260,000 miles and runs really well, except for this pretty big problem. It charges fine in around-town driving, but within 5 miles on the interstate (going 60-70) the meter display is down to one purple bar. With a light foot I can keep the display's green arrow going from the motor icon to the battery's a good part of the time, but it shows no significant recharging. Exit the highway and drive rural surface roads and in town, and the blue bars can come back, even up to five or six.
    The car has been acting this way for most of a year. It's had the ABS unit replaced and the brakes checked/serviced 2 months ago; a new 12v battery and engine checkup six weeks ago; and a rebuilt hybrid battery swap three weeks ago, all to no avail.
    I should also mention that the car sat nearly idle most of last fall/winter, due to my knee injury; I did start it a few times, and charged the 12v on a trickle charger several times, and drove it a few miles two or three times. This neglect seemed to cause no harm, and I resumed fairly regular driving in the spring. However, this problem was going on months before the period of inactivity.
    I've read posts and watched videos 'til my eyes are bleary, and talked to a few techs who basically try throwing ideas around, hoping something'll stick, but no help.
    Whadda you think? Thanks much in advance.
     
    #1 Glassmandave, Sep 23, 2025
  2. PriusCamper

    PriusCamper Senior Member

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    I'd put my bet on corrosion on first pin inside battery ECU giving bad readings and making the car's computers think the battery has lost charge even though it hasn't.
     
    #2 PriusCamper, Sep 23, 2025
  3. Hayslayer

    Hayslayer Active Member

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    I don't think that's a safe bet. I'm not sure how the connector/pins would know if the car was on the highway or a side road.

    Sounds a lot more like the engine is low on power, like it has an inlet air restriction or exhaust restriction, preventing the engine from making enough power at higher load conditions. Reduce speed (load) to a side road and all is fine. Very common symptoms for an engine that is breathing though a straw. It can run all day under low load conditions, but put it under high load? Can't handle it.

    Stick a straw in your mouth for breathing, sit in a chair and watch tv, you can do it all day. Now get up, keeping the straw as your only way to breath, go outside and run 2 miles. Let me know how it goes.

    It would be worth inspecting the air cleaner, housing, and inlet air tube system for obstruction, like a mouse nest. That would be the easiest thing to do right now. You could even just remove the air cleaner cover and filter and take it for a drive to see if it feels any different.

    A problem on the exhaust side is a bit more of a pain in the backside.
     
    #3 Hayslayer, Sep 23, 2025
    Last edited: Sep 23, 2025
  4. Glassmandave

    Glassmandave New Member

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    Thanks Hayslayer, this makes sense, and gives me a new direction to explore. Would an O2 sensor acting up contribute to the overall problem (forgot to mention I'm getting a P2238 code)?
     
    #4 Glassmandave, Sep 25, 2025
  5. PriusCamper

    PriusCamper Senior Member

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    To clarify, there's a known problem with that first pin inside the ECU once it is covered in corrosion because it causes bad readings that lead to a sudden drop of near full charge down to one or two bars that quickly rise back up to a full charge.

    While I have a few times read of symptoms of a drop down to one or two bars only at freeway speed that is not related to this problem, my hunch is to start with looking inside the battery ECU to confirm that's not the problem before doing more diagnostics.
     
    #5 PriusCamper, Sep 26, 2025
  6. Glassmandave

    Glassmandave New Member

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    PriusCamper, do you mean the ecu that is contained within the hybrid battery cover, and in unit with the battery? I just had a new...well reconditioned, hybrid battery swapped in three weeks ago, and I'm guessing a different battery ecu along with it. Also, the guy who did the swap (Motorcells, in Noblesville, IN--thanks, Chad) is top-notch, with an excellent reputation. I doubt he'd have missed a corroded pin when he was assembling the unit. Still, it's worth a check.
    Or is the one you're talking about located somewhere else?
     
    #6 Glassmandave, Sep 27, 2025
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