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0v - 74v readings? Also p0b74 any ideas

Discussion in 'Gen 3 Prius Technical Discussion' started by Prius3liang, Nov 4, 2020.

  1. Prius3liang

    Prius3liang New Member

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    So I have a gen 3 Prius that I just rebuilt battery on. I'm getting an error code randomly at p0b74. I can reset and we'll take sometimes hundreds of miles to come back on. Weird thing is I'm getting zero volts and up to 74 volts on. These readings are very short-lived less than a second. I don't know what it's causing the spikes or drops. A highly doubt the battery is actually reaching these voltages. I believe it is either smart battery indicator reading wrong or improper signals. Any ideas has anyone else ever experienced this. I Have checkes to make sure that all the battery terminals are tight etc. And I don't see any loose control wires.
     
    #1 Prius3liang, Nov 4, 2020
  2. Prius3liang

    Prius3liang New Member

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    I also forgot to mention this is per block not the whole pack
     
    #2 Prius3liang, Nov 4, 2020
  3. PriusCamper

    PriusCamper Senior Member

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    Fairly sure I've not seen that code before. But I can tell you that the most common Prius problem related to this symptom is corrosion in the voltage sensing harness, especially in the plug socket where it connects to the ECU. So have a look at that plug and clean the pins on it... In some cases the corrosion gets so bad that it fries the plug and the battery ECU, but a used ECU is only $50 and a new voltage sensing harness (Wire Frame No. 2) is $50 as well...

    I've also seen terminals break on that harness which leads to warning lights and intermittent problems with voltage readings.
     
    #3 PriusCamper, Nov 4, 2020
  4. Prius3liang

    Prius3liang New Member

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    Okay I will give all of that a try and report back, when you say ECU you're talking about the smart battery unit attached to the actual HV battery correct? 99 percent of the time the readings are perfect between .1 .2 volts of each block
     
    #4 Prius3liang, Nov 4, 2020
  5. PriusCamper

    PriusCamper Senior Member

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    yes, the battery ECU inside the electronics case that's connected to the battery pack...
     
    #5 PriusCamper, Nov 4, 2020
  6. Prius3liang

    Prius3liang New Member

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    Thanks for the help going to give this a try we'll report back
     
    #6 Prius3liang, Nov 4, 2020
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  7. Prius3liang

    Prius3liang New Member

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    Two
    Sorry for the late reply turns out there was a bolt loose on one of the battery terminals, I believe the voltage readings were actually from a bad OBD2 adapter.
     
    #7 Prius3liang, Nov 15, 2020
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