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  1. #1

    Default Strange Problem with '03 Yukon XL

    I have a 2003 GMC Yukon XL 4x4 with the 5.3L Flex Fuel motor. 3 weeks ago it was throwing lean codes for both banks so I took it in and had the intake gaskets replaced(old ones looked like ****). Just yesterday when I fired it up the battery light came on and the dash read "Battery Not Charging" then right after it said "Service Brake Booster". I took it to an O'reilly's and they said the battery is fine but the alternator is only putting out 11 amps. Could a bad alternator cause both those issues? I understand that electrical problems like alternator/battery can cause all types of codes but there was a noticeable vibration in the brake pedal after the "Service Brake Booster" warning came up. Another issue, now that I'm alternator shopping every site I pull up is showing 105 and 145 amp alternators for my vehicle saying both will fit. I contacted a couple GM dealership parts departments (in Hawaii since they're the only ones open this late) and had 2 tell me to get the 145 and 1 said the 105 is the standard one. My local Advance Auto can get me the 105 amp for $89.99 tomorrow but can't get the 145 amp one for 4 days and it's $149.99. Could I get away with the 105 amp or does the truck call for a 145? I can't find anything online that helps me. Thanks!!

  2. #2
    Master Mechanic TexasEdition's Avatar
    Join Date
    Dec 2010
    Texas Hill Country


    I believe the 105 amp is the usual standard for 2003-2004 and yes, it could cause those types of problems. See what the part # and amps are on your current alternator. There is usually a label on the alt that shows it. You could also compare the 105 and 145 amp alts at O'reilly to see if the casings are the same. I think they are. I've had 2001's, 2003's, 2005's, 2009's and 2010's....after a while they all run together (at least in my pea brain) so I may be confused as I am working from memory here.

    2009 Tahoe LTZ (Blue Granite ext/
    light & dark cashmere int)
    5.3L Vortec V8 6 speed trans.,
    HD towing, Leather interior,
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    2010 Silverado LT Texas Edition
    (Black ext/Light titanium-ebony int.)
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