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Battery voltage gauge seems inconsistant

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by jeremyc, Sep 26, 2012.

  1. jeremyc

    jeremyc New Member

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    Hey all. I am new to this site and recently purchased a 2012 Silverado Z-71 with the All Star Edition. I noticed my battery gauge needle is moving more than I have ever seen one move before. It appears the needle fluctuates between 12 and 15 or volts. The battery gauges on most vehicles I have owned stays around 13 to 14 volts and doesn't move much unless something that consumes a lot of power is turned on. Mine does this with nothing additional running on the truck other than the radio and a/c.

    This morning the needle was about 1 volt below (13 volts) the middle mark (14 volts) on the gauge. I noticed it, turned the truck off, restarted the truck and the needle went about 1 volt above (15 volts) the middle mark of 14 volts.

    Has anyone else noticed this in their trucks?

    BTW, this won't be my first post, gain info, then bail out. Someone pulled out in front of me and totaled my 84 GMC truck. I was/am very active in another forum that was started primarily for older trucks. Nonetheless, that truck is gone and I am looking for new forums to get involved with that have lots of info for newer trucks.

    Thanks!
    #1
  2. tbplus10

    tbplus10 Moderator

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    Jeremy if you look in the owners manual it can explain the system much better than I can but your 2012 truck has a variable charging system that only produces the current needed to operate electrical systems on at any one time and perform a trickle charge/maintenance charge on the battery.
    If I remember the section your looking for will either be labled "Charging system", or it might be under the gauge description.
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  3. jeremyc

    jeremyc New Member

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    Thank you for your response! I didn't read the manual word for word from cover to cover, but I did spend about 15-20 minutes skimming through it. I just now found the section that discusses this on page 5-18.
    #3
  4. Pikey

    Pikey Moderator

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    My 05 does the same thing with a new alternator and battery. In the city it is around 14 volts, when I get on the highway it drops to 11-12 volts. If I put all 4 windows up at the same time the lights dim for a second and then the voltage goes up to 14-15 volts. As soon as I let go of the buttons it drops back to 11-12
    Last edited: Oct 2, 2012
    #4
  5. j cat

    j cat Active Member

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    the guage on my 2000 silverado and the 2002 stays at the 14 volt point with the engine running and very rarely moves off this reading.

    when the alternator regulator started to go the voltage would drop to just above 12 volts then jump back to 14volts.

    Using a dc volt meter measure the alternator output voltage, compare with the dash guage.

    load up the electrical system all on see if it holds or drops.

    just because its new does not mean the battery is good, or the connections to it are in need of cleaning and securing.

    could also be a defective alternator,dash guage, or wiring.
    #5
  6. CanSkan

    CanSkan New Member

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    Both my 2012 and my buddy's 2012 do the same thing.... dealer explained to him that it is a fuel saving feature.... alternator only runs when required then shuts down to save load on vehicle and thus better gas mileage.... hope their right.
    #6
  7. j cat

    j cat Active Member

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    the load on my 2000 SIL is about 66AMPS with the engine running . If the alternator cycles on and off the Battery is going to suffer.


    I guess it is possible the alternator output is throttled to limit its output and reduce load on the engine. that would not save you much on power/MPG.

    If true this would be something to check out.
    #7
  8. WorthFlorida

    WorthFlorida New Member

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    My 2012, 1500 5.3l with less than 1K miles also does this. The seond day of ownership the battery died becuse it wouldn't hold a charge and was replaced by the dealer. I then noticed that the voltage at times would be around 13 volts. After restarting the engine it would go to the 15 volt area. The manual is 584 owner manual size pages in pdf format. About 240 pages in standard 8.5'x11" and I havn't had time to read all of it. I'm glad I joined this forum for it saved me a trip to the dealer.
    #8
  9. j cat

    j cat Active Member

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    with your dash guage readings it is quite possible they have a bad batch of alternators. high voltage will also damage a battery as well as the electronic devices/PCM.

    15volts would be if it was zero deg F air temp on a cold start. this woulld only be at that amount for a short time. the higher voltage heats up the battery quicker. a battery must be warm to accept a charge.
    #9
  10. the phantom

    the phantom New Member

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    I also have read (I believe in the owners manual) that the charging system does vary. I have noticed that my 2011 does do this so what you are describing is normal. I am sure that there are not a bad batch of alternators as someone has previously suggested.
    #10
  11. j cat

    j cat Active Member

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    I have checked into this voltage issue. the PCM turns OFF the alternator when in the fuel saving mode. this is not at all good for the battery . the constant charge / discharge will shorten the batteries life . GM however can claim that these vehicles get XXX MPG.

    Another reason for ME to not buy these vehicles.
    #11
  12. tbplus10

    tbplus10 Moderator

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    Over charging the battery is even worse for it, and whether you know it or not your present truck allows the battery to charge and discharge in the same manner only it uses the voltage regulator to do this instead of freewheeling the alternator. Doing the same thing only in a different manner and making the engine more efficient.
    #12
  13. dpeter

    dpeter New Member

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    Nothing is free. The fuel you save while not charging will HAVE to be spent on the extra power used to recharge. They get to claim fuel savings in that mode and I am sure they do but you can't stay there forever and when you come out of it, extra fuel wil be used to drive an alternator under a heavier load while recharging.
    Seems a poor choice to stress alternator and battery for PR and have the customer still pay for the gas and replace components prematurely. I would love to see the test data that proves me wrong.
    #13
  14. j cat

    j cat Active Member

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    I agree with this 100% ! your stressing out both the battery and alternator.

    The regulator over many decades now has been controlling the battery charging quite well.

    I get 7 years on my batteries. then replace. working or not.
    #14
  15. WorthFlorida

    WorthFlorida New Member

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    I'm sure the alternator is working correctly. The defective battery was charged for 90 minutes and then load tested. The electrical system had to also be tested to be sure that the battery was getting a charge. GM builds 9 million vehicles a year, that is a lot of batteries and to get a bad one out of the box is quite probable. The heat in South Florida really beats up the lead acid batteries. If you get five years from any battery you're lucky. I've lived in South Florida for 22 years and of all the cars and trucks I've own an average of three-four years is normal. I've not have paid a full price on a battery for years. I buy the six year warranty units and they always get prorated.
    #15
  16. billnorman

    billnorman New Member

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    What you're seeing is "normal". I watched mine and it seemed to only charge at 12 volts. Took it back to the dealer he told me it was OK. Two days later the battery went dead. They fixed something it now has 100,000 miles on it and reads higher than 13v most of the time.
    #16

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