Techstream shows battery voltage and SOC not in sync

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ilbdarned5, Jul 16, 2025 at 10:24 AM.

  1. ilbdarned5

    ilbdarned5 Junior Member

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    My battery charge display would sometimes show only 1 bar and randomly I would throw a generic P300 and P080 code.
    If I unplugged the battery module to reset it,( without the engine starting to charge the battery),when I power up the car the bars on the display would jump up to show a full charge.

    I realized at that point my SOC ( state of charge) in bars on my display was not showing to be in sync with the actual HV battery voltage. The bars seemed to stick sometimes throwing the codes.

    Since the HV battery module senses the battery voltage by using 14 inputs, and the input voltages are reading normal, but the SOC did not follow the voltage changes in the charge and discharge cycles. I am assuming the module is bad.

    The HV battery module seems to communicate % of battery SOC to the can bus system instead of battery voltage.
    I am assuming the module is bad, guess I will try changing it but I probably need to check the CAN BUS Pins on the battery HV Module and Main module first to see if the fault could be by a bad can bus connection.

    My question is, if all connections between the modules are good, when the battery voltage and SOC of the battery are not staying in sync, would that be a problem in the HV battery Module?
     
    #1 ilbdarned5, Jul 16, 2025 at 10:24 AM
  2. ilbdarned5

    ilbdarned5 Junior Member

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    I meant my car was throwing a P3000 code not P300
     
    #2 ilbdarned5, Jul 16, 2025 at 5:53 PM
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    When you disconnect the 12V battery, you reset the high voltage ecu (ie, give it "amnesia"). The default value for SOC is 60%, and it takes some operational time (ie driving) before the ecu can relearn the correct value.

    P3000 and P0A80 together likely indicate a failing battery module. Looking at freezeframe data from the code can help narrow down where the problem is.

    Often a bad battery module will show as a block that has 1.0 - 1.5V lower than the rest when accelerating hard

    Posted via the PriusChat mobile app.
     
    #3 mr_guy_mann, Jul 16, 2025 at 8:09 PM
    Brian1954 likes this.
  4. Brian1954

    Brian1954 Senior Member

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    What year is your Prius, and how many miles?

    Has the hybrid battery ever had work done on it, or has it been replaced before?
     
    #4 Brian1954, Jul 17, 2025 at 12:04 PM
  5. ChapmanF

    ChapmanF Senior Member

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    Although it's generally true that the overall voltage is higher at higher states of charge, there isn't a simple relationship. The curve relating the two is pretty close to flat for a spell in the middle.

    The battery ECU also monitors a current sensor, so it can track the coulombs of charge in and out of the battery, for a better idea of what the state of charge is at a given time. When memory power is lost, that gets forgotten, and then the ECU has to start off with a rough guess of SoC only based on the voltage.
     
    #5 ChapmanF, Jul 17, 2025 at 2:38 PM
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