Diagnose a bad/dying 12volt with scan gauge?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by littlehandegan, Jan 8, 2015.

  1. littlehandegan

    littlehandegan Junior Member

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    When using the scanguage reading volts, how would one note failure, dying of the 12volt?
     
  2. bisco

    bisco cookie crumbler

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    under 12.4 volts, after car has been off for a few hours.
     
  3. edthefox5

    edthefox5 Senior Member

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    Car will always show 13.8 to 14 volts when car in ready
    Which is charging voltage. So disregard that.

    U need to measure the battery first thing in the am before u start the car.

    Try installing the SC and going into accessory mode which us foot off brake and 2 button pushes.
     
  4. littlehandegan

    littlehandegan Junior Member

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    Accessory mode indicates 10.8-11 vlt
     
  5. Easy Rider 2

    Easy Rider 2 Senior Member

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    I am surprised that the car still starts.
    You are WAY past needing a new battery.
     
  6. littlehandegan

    littlehandegan Junior Member

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    I am correct is saying accessory mode is when I turn the car off, then with my foot off the brake I hit the button twice?

    My fan and stereo comes on along with dash lights. And it reads 12 then goes down to about 10.3 fairly quickly with the stuff on. However, when I turn off the car the scanguage indicates 12.0 vlts

    Ok so checking using the vehicle signal check mode it is 11.8 and stays there
     
  7. Easy Rider 2

    Easy Rider 2 Senior Member

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    11.8 is not enough with no load; neither is 12.0.
    With no load the battery needs to be at least 12.4 and even that would indicate that it is getting a bit weak.

    ALL of your readings indicate a bad battery........or one that isn't being charged long enough or often enough.

    The only way to tell for sure is to charge it externally with an automatic charger and then take readings again.
    If it is over 4 years old, you might as well just replace it.
     
  8. GregP507

    GregP507 Senior Member

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    I've never seen so much agonizing over anything so much in these forums as the 12 v aux battery. It's almost too simple to prescribe: If your battery goes dead much sooner than you expect, have it tested by someone who isn't biased in favor of selling you a new one, whatever it's condition.

    If it checks out, stop fretting, because as long as it starts the car, it's fulfilling it's role in the system 100%.

    P.S. By "start the car" I mean turning on ready-mode.
     
  9. valde3

    valde3 Senior Member

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    But if you check battery voltage in acc mode with MFD it isn’t no load condition. MFD and some other parts of car are draining battery so a bit lower voltages (compared to no load) are ok.
     
  10. bisco

    bisco cookie crumbler

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    do what ed said in post #3.
     
  11. Easy Rider 2

    Easy Rider 2 Senior Member

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    Not true.

    Many people have been down that road and advice like yours has caused them untold grief.
    If the car only "starts" part of the time, it still could be a bad battery......regardless of the "test".
    If it comes on accompanied by various, seemingly unrelated trouble lights and codes, it still could be a bad battery......regardless of the "test".

    The simple fact of the matter IS that the standard CCA test is not good enough and never has been really.
    In a conventional car, the "starter test" was much better; almost fool-proof.
    A hybrid does not have a "starter test" so other indications are needed.

    Ignoring those other indications is just foolish. (Yes Greg, I mean YOU.)

    I will stop taking you to task for posting this........when you stop.
    It is bad advice.

    That's why I much prefer a $10 multimeter. Better control over the conditions.
     
  12. Mendel Leisk

    Mendel Leisk Titanic Social Director

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    Get a multimeter, check your 12 volt battery's voltage, with the car right off. It's not a load tester, but it will give you a decent idea of the state of charge.

    A multimeter indispensable for so many things, even to check all the batteries (AA, D, etc) knocking around in your tool drawer. Or to make sure the power's REALLY off, when working on household wiring.
     
  13. GregP507

    GregP507 Senior Member

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    Yes, we've been down this road many times, and your opinions are well-known; so are mine. I'll continue to use my battery until it no longer activates the circuit that boots the computer into ready-mode.

    That should be a long time in the future, because I don't use acc-mode at all, therefore my battery never needs to cycle, which shortens it's life. If I see any signs that the condition of the 12 v aux battery is having any sort of effect on the car, I'll be sure to let you know, and I'll be the first to admit my mistake.
     
  14. Easy Rider 2

    Easy Rider 2 Senior Member

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    My training and life's work is in Electronics.
    Yours is in agriculture and the environment.
    Which opinion on batteries and electronic equipment do you think should carry the most weight ??
     
  15. GregP507

    GregP507 Senior Member

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    IdontCare.jpg
     
  16. Easy Rider 2

    Easy Rider 2 Senior Member

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    That's no surprise.
    In order to care, you have to be able to actually think.
     
  17. edthefox5

    edthefox5 Senior Member

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    BadaBing!
     
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