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  1. #1

    Default 09 avalanche charging system low voltage

    I'm just bought an 09 Avalanche LTZ 6.0L a few weeks ago. The volts gauge was rock steady at 14 volts until this weekend when I noticed it down at 12.5 or so. I watched for 30 min on the way home with the intention of checking the voltage when I arrived. Just before I got home the gauge moved back to 14. I tried starting and driving it again and it never moved off 14. This was daylight driving with the ac on so nothing should have been cycling on and off. This morning I head out for work and I see the volt meter showing 12.5 or again. I get to work and check it with a muiti meter and sure enough its reading 12.65. I hooked up to a Snap-On D tec tester (for charging systems, starters and batteries) and checked it out. The voltage was 12.7 and the tester said the alternator was good (no bad diodes).

    So my question is, is the low voltage normal? I'm used to a charging system holding the voltage at 14 or so and increasing amp output as required.


  2. #2


    No, it is not normal.

    If the alt is testing ok (and, a proper test is out of the truck on a test stand), the battery must have a bad cell. It should be load tested.

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  3. #3

    Enkeiavalanche's Avatar
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    Apr 2010
    Piermont,NY, back in Northern NJ now, But may be in IL soon....


    They will Flex a bit.. Unless it goes below 12.4 I would not worry about it much.. If it is hard starting too look into a new Batt. I may get one for my 08 before the winter comes.. Click image for larger version. 

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    08 Z71 Avalanche Mods to date: K&N CAI,Hellwig Swaybars and End Links, Corsa Sport Exhaust, Superchips Programer,IPCW LOF & 3rd brake light and tails, AMI Gas door,Show Hooks and Door locks, Enkei Wheels, with Pirelli tires, StreetScene Bowties, Grant Steering wheel,Muth signal mirrors,SSBC Big Brake kit,Huskyliner Mug gards,Floor mats and Hood shield, McGard Lug nuts and locks, Bedrug, Cervini's Ram Air hood,35watt HID Fog lights, Sylvania bulbs all around ZXE's Highs and Lows, WhiteNight Back up lights,Sirius and HD Radio, SnugTop sitting on deck now Got a Softopper on now,Tempress Boat Hatches.... New Bilstein shocks are on... New Mods coming soon..... X

  4. #4


    Check your battery connections. I had the same problem with my '03. It was in the red plastic jumper cable access box.
    "It went together didn't it? Well then there has to be a way to take it apart!" - Me.

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  5. #5


    Does anyone know if the voltage regulator is in the engine ECU, body control module or the alternator itself? The alternator tested OK on a Snap on tester but that only means there are no bad diodes or winding's so I'm thinking the voltage regulator has a issue.

  6. #6


    The regulator is in the alternator.

    A fully charged battery reads 12.5 volts. Perhaps, your regulator is doing what it is being told to do.

    Some of the GM trucks (my old Envoy was one), are controlling the charge voltage a lot closer than the alternators of old.

    On a cold winter morning, my old truck would not let the alternator charge for the first 30, or so, seconds after starting. I have a lot of guesses, not been able to find the real reason.

    I suspect, in the name of fuel economy, the alts in today's trucks may be turning off the charge current when the truck voltage reaches 12.5, turning it back on when the voltage drops. Of course, this is what the alt/reg has always done, all I'm saying, is that the PCM may be monitoring the charge a little more than it did in the pre CAFE day.

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