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Testing Battery/Alternator Voltages - Multimeter or OBDII Code Reader???

Discussion in 'Technical Chat' started by Ninjalicious1985, Nov 25, 2015.

  1. Nov 25, 2015 at 5:37 PM
    #1
    Ninjalicious1985

    Ninjalicious1985 [OP] Well-Known Member

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    Hello there,

    I was using an Innova 3100 code reader to perform a test of the battery and alternator. The results of each test had a message attached to it saying that the voltage were below what they are supposed to be.

    Battery Monitor Test: 11.20V (engine OFF)
    Alternator Monitor Test: 12.55V (with all accessories on and running engine above 2000 RPM)

    After getting these results, I hauled out my digital multimeter and performed the tests again. I then got the following results:

    Battery: 12.4-12.5V (engine OFF)
    Alternator: 13.6-14.0V (with all accessories on and running engine above 2000 RPM)

    So my question is: which tool should I trust?

    Cheers!
     
  2. Nov 26, 2015 at 3:28 PM
    #2
    Wyoming09

    Wyoming09 Well-Known Member

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    Did you use both at the same point where you plug into the OBII port.

    They are both correct !!

    The first is voltage drop going through the wiring and ecm to the port.

    Second is most likely direct from battery terminals Correct ??

    Myself I would rather use the Multi Meter more points for testing
     
  3. Nov 28, 2015 at 2:56 PM
    #3
    Ninjalicious1985

    Ninjalicious1985 [OP] Well-Known Member

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    Yes. I used the MM directly on the battery. Your explanation on voltage drop makes sense. Thanks!
     
  4. Nov 28, 2015 at 3:00 PM
    #4
    KenLyns

    KenLyns 8.75" Third Member

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    Multimeter is more accurate. The ECM doesn't need to "know" the precise voltage for any of its normal functions, only for startup protection against a drained battery.
     
  5. Nov 28, 2015 at 3:15 PM
    #5
    Ninjalicious1985

    Ninjalicious1985 [OP] Well-Known Member

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    Makes sense. Nice to know that my battery and alternator are still good. Thanks!
     
  6. Nov 28, 2015 at 3:21 PM
    #6
    Clearwater Bill

    Clearwater Bill Sometimes when I close my eyes, I can't see.

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    While the multimeter is the best, my Scanguage II gives an exact match to the alternator output.

    I'm not aware of any battery monitor testing available via the Scanguage. (someone educate me if there is)
     
  7. Nov 29, 2015 at 1:58 AM
    #7
    Wyoming09

    Wyoming09 Well-Known Member

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    With the way this electronic stuff changes I know I can`t keep up .

    I mean really self driving cars
     

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