Battery wiring help needed.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Prius92, Jul 24, 2025 at 9:53 AM.

  1. Prius92

    Prius92 Active Member

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    I've had to have it jumped twice now and almost towed.
    Battery is fine, measures 12.5 volts. Had it tested at autozone too.
    But when I use Dr. Prius, it says the 12v is only 11.5, which is too low for it to go into ready mode.

    Where does this measurement occur at?

    I checked the positive and ground at the battery, it's fine. I get 12.2v at the jumper junction under the hood, all 3 were fine, no corrosion, not loose.
     
    #1 Prius92, Jul 24, 2025 at 9:53 AM
  2. Prius92

    Prius92 Active Member

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    When I checked the battery at the headunit (headlight on/off 3x) it shows 12.3v.
     
    #2 Prius92, Jul 24, 2025 at 10:05 AM
  3. Tombukt2

    Tombukt2 Senior Member

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    The .2 and .3 are getting down they're for this AGM type!
     
    #3 Tombukt2, Jul 24, 2025 at 10:27 AM
  4. ChapmanF

    ChapmanF Senior Member

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    Pin sixteen of the OBD-II connector has 12 volts at all times. Many dongles provide a voltage reading by actually measuring that—not by asking any ECU in the car for a reading.

    It does seem as if there might be a substantial voltage drop between the battery and other stuff ... I'm not used to having much trouble going READY unless voltage drops below 8 or so.
     
    #4 ChapmanF, Jul 24, 2025 at 4:03 PM
  5. Prius92

    Prius92 Active Member

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    The other odd thing I noticed is when it's acting up, the car beeps when you open the door until you close it.
     
    #5 Prius92, Jul 24, 2025 at 4:08 PM
  6. Prius92

    Prius92 Active Member

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    I think I have it fixed. Pulled the connector out of the Transmission Control Unit and some of the metal was corroded, sprayed it with contact cleaner and brushed it. So far, so good. Oddly the pins on the control unit itself were still shiny.

    [​IMG]
     
    #6 Prius92, Jul 24, 2025 at 4:49 PM
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