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Voltage Reading from Fuse Box +12V Cleat to Ground When 'Running'

Discussion in 'Prius v Technical Discussion' started by Air_Boss, Jul 4, 2016.

  1. Air_Boss

    Air_Boss Senior Member

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    On a 2012 Prius v Five...

    What voltage should be present from fuse box nominally +12V guarded 'cleat' to ground?

    I would have thought +13.8-+14.2V (over +12.8V) when the inverter is operating, but I only see +/- +12.8V.

    ??
     
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    My Scangauge II shows 14.4 v but I do not have a multimeter.
     
  3. Air_Boss

    Air_Boss Senior Member

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    Thanks. Hmmm.

    Where on the bus does the scangauge read?

    Any reason to believe the guarded cleat to ground reading would be different?
     
  4. bisco

    bisco cookie crumbler

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    i'll check mine. the cold reading yesterday morning was 12.87
     
  5. bisco

    bisco cookie crumbler

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    mine reads 14.57 at the fuse box, car in 'ready', that is, foot on brake, press power button once.
     
  6. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    It is a data value on the OBDII bus perhaps in the inverter. The cleat in the front fusebox is attached to the battery by a long, large cable
     
  7. Air_Boss

    Air_Boss Senior Member

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    Weird. +12.83 volts cleat to ground in READY mode..
     
  8. bisco

    bisco cookie crumbler

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    huh, i wonder if pip is different.(n)

    what does it read with the car off?
     
  9. Air_Boss

    Air_Boss Senior Member

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    Roughly same, +12.6 to +12.8V depending on state of charge.
     
  10. bisco

    bisco cookie crumbler

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    interesting. hopefully, someone with a v and multi meter will check.
     
  11. rjparker

    rjparker Tu Humilde Sirviente

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    Voltages on my 2012 v, I get 12.7 vdc when system is off as measured at the fuse box takeoff, 11.7 when ON and AC/Lights on but not in ready, and 14.27 vdc when in Ready Mode with AC and lights on.

    The car had just been run about 50 miles 15 minutes before my measurements, so the12v battery probably did not need much charge. I would consider an inverter problem with no real change from off to Ready. Is it actually coming on and saying Ready?
     
    #11 rjparker, Jul 4, 2016
    Last edited: Jul 4, 2016
  12. Air_Boss

    Air_Boss Senior Member

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    Oh, yeah, and there is no indication of a lack of 12V maintenance charge, either.

    This is just (and all) about being unable to use a module that senses >13.2V to trigger a relay to power an accessory.
    .
    Frustrating.
     
  13. bisco

    bisco cookie crumbler

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    ya, that kine of stuff in a prius is tricky.
     
  14. xliderider

    xliderider Senior Member

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  15. Air_Boss

    Air_Boss Senior Member

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    Using that delay relay requires finding a source of +12V with IG2 "on", which has been elusive.
     
  16. gafortiby

    gafortiby Member

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    You could just tap into the fuel injectors or ignition coil circuit. Those are only energized when ig2 is energized. Is IG2 normally open or normally closed? You know what I mean.

    Apparently you can also tap off the washer fluid pump or inverter.
    Highbeam 50% DRL mod, completed | Page 3 | PriusChat
     
    #16 gafortiby, Sep 23, 2016
    Last edited: Sep 23, 2016
  17. gafortiby

    gafortiby Member

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    A safer but not as satisfying solution would be to tie into glove box light circuit which is always and only on when headlights are on.

    If you had a 2014 then I would have also said the DRL circuit but I think your 2012 doesn't have DRL.
     
  18. ChapmanF

    ChapmanF Senior Member

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    Those gadgets (like the InPower VCM-06) typically work great in a Prius.

    Something very peculiar seems to be going on with your particular Prius. You can see that the others responding to your question are doing the same measurement and getting the expected value (high 13s to mid 14s when the car is READY ON).

    Before diving too deep into possible explanations why your Prius is different ... are you sure it is READY ON when you make this measurement?

    -Chap
     
  19. ChapmanF

    ChapmanF Senior Member

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    When a ScanGauge shows 12 V bus voltage, it may be measuring directly. One of the standard OBD-II connector pins is specified to be an unswitched 12 V supply. (This is why caution is recommended when probing pins in that connector, even if the car is off.)

    -Chap
     
  20. Air_Boss

    Air_Boss Senior Member

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    Turned out to be an open GROUND in the relay harness driven by the >13.2V sensor. One strategic splice later, works fine.
     
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