Gen 1 2003 Prius Hybrid Battery Problems

Discussion in 'Generation 1 Prius Discussion' started by Ethan Gueck, Jun 28, 2025.

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  1. Ethan Gueck

    Ethan Gueck New Member

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    Dallas, TX
    Vehicle:
    2003 Prius
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    N/A
    I got a 2003 gen one in Feb 2024 with 77k miles on it and garage kept. It was nice. Previous owner had every receipt for every piece of maintenance and repairs done including a remanufactured hybrid battery in October 2022.

    a few months after I got it, the triangle of death light came on. I checked the code and it was P3001 Battery ECU. After a little bit the lights went away in its own. A few months later, it happened again. I went to EBay for a new battery ECU and after installing realized I replaced my 89890-47030 with a 89890-47060. Went to Facebook and people said it would be fine.

    A few months later the code came back, and went away once again. This now happens every few months. I’ve noticed it seems to happen if the car sits for 5 days or more, or if I’m only taking it on very short trips. I don’t notice any issues with the way the car runs. MPG is the same, and everything seems to work as usual. I just keep getting code P3000-123 Battery Control System, and code P3001 Battery ECU.

    Is it possible that I installed another battery ECU that is also bad. Or is there something obvious that I am missing? Dealer wants $200 to diagnose it, but I fear they will just pull the codes and tell me what I already know. They also said it won’t be under warranty because the battery was an after market reman and not a Toyota battery so it’s a 1 year not 3 year warranty.

    Does anyone have any insight on where I should start? Should I put another eBay computer in it? Should I pay the dealer to diagnose? What do yall think? Thank you!!
     

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    #1 Ethan Gueck, Jun 28, 2025
  2. Tombukt2

    Tombukt2 Senior Member

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    Vehicle:
    2009 Prius
    Model:
    Base
    Is the battery ECU on the Gen 1 Similar to the 2 ie you can open back cover and see all the yuk inside ? That ever happened ? Maybe take a look inside . All my Gen 2 orange receptacle BCM are crappy looking inside once cleaned up I haven visited again . So uhhh maybe
     
    #2 Tombukt2, Jun 29, 2025
  3. Josey

    Josey Active Member

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    Location:
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    Vehicle:
    2003 Prius
    Model:
    One
    Opinions about this vary...but you said it seems to happen if the car has been sitting for 5 days or more. Monitor the voltage of your 12V battery. I owned a 2003 for like 7 years. Only had problems if the 12V ran down and it would if it sat for days at a time. I think I had a small parasitic draw, but never did figure that out.

    No matter. If you want to keep this car on the road DO NOT let it sit for days at a time. For the sake of the batteries - 12V and hybrid pack - it needs to be driven very regularly. At the very least, get a trickle charger for the 12V.
     
    #3 Josey, Jul 3, 2025
  4. mroberds

    mroberds Member

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    Like Josey, I will cast aspersions on the 12 volt battery. Do you have a record of when it was changed? (For a 2003, even with low mileage, it's been changed at least once.) If it's 10+ years old, get another one. :)

    I don't really recommend this, but it's possible to open up the battery ECU and see if there's any obvious mayhem inside. You have to take it out of the HV battery first - nothing plugged into it at all. You also should be at an ESD workstation - at least wear one of those wrist straps to ground. It's possible for a couple of the capacitors in it to be charged to +280 V DC, so don't poke random things. They're only a few microfarads, but they will bite.

    You are looking for things like dead bugs inside it, burnt spots on the circuit board, corroded pins on the external connectors, random dust and crap. The entire high-voltage circuit board is conformal coated (clear paint, as insulation), to reduce the effects of humidity.

    I took mine apart once, decided it looked like a battery ECU, and put it right back together. :D I had heard that later model years (2004-up?) sometimes had problems with the sense wire connector (the orange multi-pin one) getting corroded inside the ECU, and I wanted to see if mine was like that - it was not.
     
    #4 mroberds, Oct 5, 2025 at 12:43 AM
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