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  1. #1
    Sr. Apprentice
    Join Date
    Jan 2008
    Taneytown, MD

    Default Weak Alternator?

    I recently traded my 04 Silverado in a slightly used 08. I haven't had too many issues other than a noisy windshield which was fixed and a blown front driver side speaker. I've noticed recently when driving at night that when I apply my brakes my lights flicker just slightly. They also do this when I use anything else electrical in my truck.. blinkers, windows, etc. I wonder if I might have an alternator about to go out. Since the winter has been so mild I haven't noticed any hard starting issues. Did anyone else find they've had to replace the alternator?

  2. #2

    mfleetwood's Avatar
    Join Date
    Jul 2010
    Denver, CO
    Blog Entries


    I have a '08 as well and the same thing was just happening to me a few weeks ago. I thought it was the alternator too but when I took it over the parts store, they tested my system and said I had a couple dead cells in my battery. I replaced my battery and the headlight flicker went away. Before you change out your battery though, head down to the auto-parts store and have them test your system first just to be sure.

    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

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  3. #3
    Sr. Engineer
    Join Date
    Dec 2011
    11-22-boogie woogie avenue


    Check voltage on alt. should be 14.5 volts . Yours has the two positive post connector i think.. check it for corrosion

  4. #4


    Also check your ground between the battery and the chassis for clean contact at both ends. Bad grounds will cause the voltage to drop enough that your lights could dim from a relatively benign additional electrical draw. You also have a ground wire running between the alternator and the ground post of the battery. Check those points as well.
    1994 Chevy K2500 Silverado, 454 (modified), original owner.
    And other vehicles and toys.

    "...If you can meet with triumph and disaster
    And treat those two imposters just the same;'ll be a Man, my son!" Rudyard Kipling

  5. #5


    As stated above check the grounds for a good contact.

    An FYI for owners of 2010 and above trucks.
    If you have alternator issues on these trucks you need to follow the factory repair manual troubleshooting section religiously, some of these trucks are equipped with a charging sensing system that adjusts voltage output according to what it thinks you might need.
    The system wont always charge at 14.5 it can charge as low as 3.5 volts (which is about what it needs to run the ignition system) if it feels the system could overcharge the battery. With these trucks it's not uncommon to see readings around 9.0 volts as the system prefers to tricle charge the battery rather than a max amp charge. The idea behind the system is to not overwork the battery to give it longevity.

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