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2013 Sierra Volt meter doesn't drop from 14+ volts as designed.

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by bigjer, Jul 12, 2013.

  1. bigjer

    bigjer New Member

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    Hi everyone,
    I just took advantage of GM's huge incentives and upgraded my 09 Sierra to a new, 2013 Sierra z71. LOVEEEE it!!
    Being the stickler for details that I am, I noticed that the Variable charging rate system that fluctuated between 12-15v on my 09's volt meter(as designed) hasn't varied at all on my 2013. I only have 300 miles on the new one.
    I realized(from service manual) that many conditions have to be met to lower the voltage output, but I think I am meeting those conditions and the volt meter hasn't dropped off 14+ at all. I even topped off the battery with my C-Tek charger overnight and the battery is fully charged.
    Anyone have any info on this? Is it because of low miles on truck?
    #1
  2. tbplus10

    tbplus10 Moderator

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    No insight to repairing your problem, only confirmation that yes you should see some fluctuation on the gauge.
    I assume the truck is properly transitioning to 4 cyl mode.
    One possibility since this system is a learning system is that it might still be putting together information on how you drive. The alternator and AFM systems take quite a few miles before they settle in and operate to their full capacity.
    #2
  3. stchman

    stchman New Member

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    We want pics of the truck!!!!!

    I'll check my 2013 Silverado volt meter to see if it drops.
    #3
  4. RayVoy

    RayVoy Active Member

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    It is possible, because of the way the '09 presented the voltage readings (and, my '09 reads the same), that the needle movement was dampened on the newer trucks. Maybe GM just got tired of people asking "how come the voltage gauge readings constantly change"?

    I would run a couple of wires from the battery into the cab and connect a hand-held volt meter. Have someone drive and you compare the DVM to the dash gauge.
    #4
  5. GM Customer Service

    GM Customer Service Member

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    Hello,

    First, congratulation on your new vehicle. I am sorry to hear that you do have a vehicle concern on your new vehicle. Private message me if I can be of assistance.

    Safe travels,

    Jennifer T.
    GM Customer Care
    #5
  6. greywolf11

    greywolf11 New Member

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    When I got my '13 back in February I noticed that my voltmeter showed a higher charging level than my '11 when it was charging. I never noticed the truck dropping back below 14 until I probably had 2 or 3 weeks driving. Now it runs at the same level as my '11 and drops back just like the older truck. As posted by others, I bet it is in some sort of learning mode.
    #6
  7. stchman

    stchman New Member

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    Ok, after replying to this thread back on 7/12 I kept an eye on my volt meter of my 2013 Silverado.

    I can say when running that meter never drops below 14V. This appears to be just the way it is.
    #7
  8. j cat

    j cat Active Member

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    my idea about this voltage/charge drop out to save fuel ??? is / was a bad idea. this just damages the alternator. best the alternator always supplies the light amount of power to run all the electrical equipment and charge the battery if required.

    drawing down the battery when the alternator drops out is also not good !
    #8
  9. stchman

    stchman New Member

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    Can you elaborate on this?
    #9
  10. j cat

    j cat Active Member

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    lead acid batteries need be charged fully at all times. when they discharge[supply power] they must be charged in a short amount of time . the more you discharge a lead acid battery [frequent starts] the shorter the life.

    when operating a vehicle and the alternator drops out the discharge frequency increases this causes damage to the cells due to heat generated when the alternator starts charging the battery. heat is what also kills these batteries. like on some of these new vehicles the battery is up against the fire wall not the best place to put a battery to avoid heat since the air from the engine/radiator is in that area.

    light loading of the alternator is best since it will reduce brush commutator wear . the windings and regulator also get damaged from the heat created with the constant hard charging of the battery so you can save a little fuel or perhaps for GM to pass some EPA mileage law.
    #10
  11. stchman

    stchman New Member

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    So basically you're saying that the current electrical setup for GM vehicles is to lightly load the alternator (thus reducing some drag on the engine) and use the battery as a reserve to improve fuel economy? My thing with that is that the battery would eventually drain to a point where it would no longer be a reserve and the alternator would have to work really hard to charge it up.
    #11
  12. j cat

    j cat Active Member

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    that is what I believe is going on. the battery MUST supply power to operate the electrical systems when going into power /fuel saving mode.

    now if this were a carb set up you do not have the higher electrical loads as we have now with more electrical components controlling/monitoring the vehicles operation.

    when the battery gets down in voltage the PCM must be turning the alternator back on and stays on until the alternator current drops off indicating the battery is charged .
    #12
  13. stchman

    stchman New Member

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    The alternator is driven by the serpentine belt. The alternator should be oblivious when AFM switches from V8 to V4.
    #13
  14. j cat

    j cat Active Member

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    the alternator is driven mechanically by the belt, sure it is, However the alternator is electrically driven by the field voltage. the greater the field excitation [magnetism] the greater the charge and the PCM does control this field voltage which is a wire on the back or top of the alternator on the connector plug.

    so that is how the volts gauge goes up and down to reduce engine load at times that the GM engineers figured out would work until the warranty ends to increase MPG a few .
    #14
  15. RayVoy

    RayVoy Active Member

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    Actually, let's call it "smart charging" (smart seems to be the catch prefix these days). Firstly, @j cat is right, heat is the killer of batteries.

    In the "old" system of charging, the alternator, using the internal regulator, kept the battery charged using 14.8 volts. On, or off. The regulator was either charging the battery with 14.8v (if it could), or it wasn't charging the battery.

    Three things are fact: electric load changes, temperature changes, and engine speed (alternator rpm) changes.

    The "smart" alternator, has the ability the change the charging voltage to match the electrical load. It also has the ability to change the charging rate to keep the battery in an 80%, or higher, state of charge.

    The whole idea is to keep the battery at an 80%, or higher, state of charge.
    The PCM can increase idle speed if the load is high and the state of charge falls below 80%.
    The PCM can change the charging voltage (maybe we only need 13.8 volts, not 14.8) and the duration, to keep the battery at an 80% state of charge.
    The PCM can turn off the charge if the temp is low (cold winter morning), reducing the spin load on the starter.
    After the start, the PCM can increase the charge voltage to quickly get the battery back to the 80% state.

    In doing all of this, the battery should run cooler, a cold engine should start easier and the reduced charging load on the engine should give better mpg.

    My 2 cents.
    #15
  16. tbplus10

    tbplus10 Moderator

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    You pretty much nailed it Ray, in older systems the voltage regulator controls whats coming out of the alternator, but the alternator load doesnt change much as far as drag on the engine, this new system in a sense allows the alternator to freewheel when it doesnt need to produce a lot of amps.
    Once the batterys charged load demand drops, turn off things like A/C, heater fan, radio, lights, load demand drops and remains low, theres no requirement to produce amps that arent used which is essentially what normsl alternators do.
    Drawbacks to this system are its controlled by the PCM which gives something new to troubleshoot or worry about failing.
    Advantages are it takes the alternator essentally offline when not required to produce power or as much power.
    This theory isnt new, ships and aircraft have been using this method for years when either max power is required or they want to go into fuel saving cruise mode. The difference in their systems is they manually select generators off-line or on line when a condition or situation dictates it.
    #16
  17. j cat

    j cat Active Member

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    these are my opinions based on the components involved and over the years with training in electrical /electronic devices and what is best for a longer trouble free life. I maybe very wrong. the alternator and battery maybe a different design to handle this type of damaging cycling.

    just to point out something stated when the battery temp is very low like on a cold 20 deg f morning and you start your vehicle the alternator output is very high . 15 volts approx. the reason for this in a old design is to heat up the battery because a cold lead acid battery cannot charge. the high voltage wakes up the battery then after 15-20 min the battery can start to recover from the cold crank cycle.

    another comment. The battery does not supply any power when the engine is running with the old design. the sole purpose of the battery is for starting the engine and to get things going with the engine OFF.

    lead acid battery's must be fully charged at ALL TIMES , if not the batery will get internally damaged.

    so IF GM has changed these components in the design to handle what is going on now with these new vehicles I would be wrong. time will reveal this with I would expect more frequent battery and alternator replacements.
    #17
  18. RayVoy

    RayVoy Active Member

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    Not for a second suggesting your view-point is wrong, like you, I also spent many years working in an environment where the lead acid battery was the life of the industry and I agree with everything you said about the lead acid battery. Salfation of the plates occurs during deep discharge and it requires a very high voltage/current to remove the salfate and return the liquid back into sulfuric acid.

    Deep discharge/recharge and the resulting heat will shorten the life of any lead acid battery.

    I wasn't taking sides, just presenting the current technology (be it good, or bad) being used by GM.
    #18
  19. j cat

    j cat Active Member

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    one thing I have learned over the years is things do change . this maybe some GM engineering achievement . could also be a big flop at our expense .

    I understand what your saying with this . good info to get out there .
    #19

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