09 avalanche charging system low voltage

Discussion in 'GM Electrical Tech' started by Phatgto, Jul 31, 2012.

  1. Phatgto

    Phatgto New Member

    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.

    Thanks!
     
  2. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    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.
     
  3. Enkeiavalanche

    Enkeiavalanche Rockstar 4 Years ROTM Winner 5000 Posts

    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.. DSCF9494.jpg
     
  4. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    Check your battery connections. I had the same problem with my '03. It was in the red plastic jumper cable access box.
     
  5. Phatgto

    Phatgto New Member

    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. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    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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