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12V battery plug

Discussion in 'Gen 2 Prius Technical Discussion' started by JohnPrius3005, Nov 22, 2022.

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  1. JohnPrius3005

    JohnPrius3005 Active Member

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    Greetings Oh Prius Technical Wizards
    Doubtless one of you can answer my relatively basic technical question.
    On top of the 12V battery is a black "terminal box" (for want of a more correct term). This box is connected to the 12V battery positive terminal.
    A relatively large white connector plug with its associated harness plugs into the front LH side of the terminal box. Removing this white connector from the terminal box isolates the vehicle from the battery positive terminal, thus removing 12V battery power from the vehicle.
    A much smaller white connector plug and its associated thin wire plugs into the front RH side of the terminal box.
    The wire from the smaller white plug, due to its small size, I'm guessing provides positive 12V contact to a sensor or sensors

    Question(s) please:
    What sensors get powered by the wire from the small white plug?
    What are the adverse consequences of disconnecting this small white plug or breaking the thin wire leading from it?

    (I won't bore you with details but I'm currently and have been for many months driving my Prius in "survival" mode. I disconnect the large white plug every time I park the car. The thin wire to the small plug broke. I noticed that I now, in addition to all the other warnings and messages, have a red battery symbol in the top LH corner of the MFD, logically because of this broken wire. What I'm looking to find out from those far more knowledgeable than me is "what does this mean?" and should I fix it before "x" happens.)

    Thanks so much in advance. This forum rocks!!
     
    #1 JohnPrius3005, Nov 22, 2022
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  2. JohnPrius3005

    JohnPrius3005 Active Member

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    !
     
    #2 JohnPrius3005, Nov 22, 2022
  3. dolj

    dolj Senior Member

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    I really don't understand the angst. You have something broken that you rightly point out causes problems. Just fix it and get on with life! If you don't have the skill to do this, take it to someone who does.
     
    #3 dolj, Nov 23, 2022
  4. ChapmanF

    ChapmanF Senior Member

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    Up under the hood, in the big silvery box, is something called the DC/DC Converter. When the car is in READY mode, the converter produces the 12 volt supply (really more like 13.8) to power the car's accessories and to recharge the 12 volt battery.

    The skinny wire back to the battery is simply to sense the voltage at that point. It goes directly to the converter up front. That way, the converter can regulate its output to produce exactly the desired voltage at the battery (instead of just regulating to its own local measurement and not knowing the voltage drop back to the battery).

    If the skinny wire is disconnected or broken, a Gen 1 will complain (as you see) and keep driving, with the converter producing a default voltage at its own output.

    If the same thing happens in a Gen 2, the car will complain and not go READY.

    In Gen 3, they stopped bothering with this remote-sensing setup. The Gen 3 converter still has a sense wire input, but they just land it right on the fusebox right next to the converter, instead of sensing back at the battery.

    As dolj suggested, the car's battery charging system will work better with that connection fixed.
     
    #4 ChapmanF, Nov 23, 2022
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  5. JohnPrius3005

    JohnPrius3005 Active Member

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    Hi Chap, Thank you very much. This is exactly what I was hoping to learn. It's an easy fix to re-attach the sense wire to the connector. Aloha.
     
    #5 JohnPrius3005, Nov 23, 2022
  6. Longinus876

    Longinus876 Junior Member

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    Is the 3rd connector for the abs? I have the triangle and when I disconnect the abs wire for about 10 seconds, the triangle goes away on restart but comes back. Any ideas why that should happen...and what's causing the red triangle?
     
    #6 Longinus876, May 25, 2023
    Last edited by a moderator: May 25, 2023
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