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Alternator

Discussion in 'Electrical' started by RobC, Feb 2, 2018.

  1. RobC

    RobC New Member

    7
    8
    Feb 2, 2018
    California
    i have a 05 GMC Yukon Denali My Voltmeter runs between 9-10 but when I turn my headlights on it goes to 14 and stays there. I did replace the alternator with one from Napa and it did the same thing. Any thoughts
     
    jrsavoie likes this.
  2. smokymtn65

    smokymtn65 Active Member

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    Aug 21, 2015
    East TN
    Verify the voltmeter is accurate first. Welcome BTW
     
  3. RobC

    RobC New Member

    7
    8
    Feb 2, 2018
    California
    How would I verify the voltmeter?
    Thanks Smoky
     
  4. smokymtn65

    smokymtn65 Active Member

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    Aug 21, 2015
    East TN
    i guess you are referencing the dash gauge . Do you have a tester(voltmeter) ? To compare the readings.
     
  5. RobC

    RobC New Member

    7
    8
    Feb 2, 2018
    California
    Yes the dash gauge. Should I put a voltmeter on the alternator?
     
    jrsavoie likes this.
  6. smokymtn65

    smokymtn65 Active Member

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    Aug 21, 2015
    East TN
    You can, best if you have probes with alligator clips or something to hold in place so you can watch the read out on volt meter and gauge at same time. there should be an exposed positive lug on you fuse box may be easier than going to alternator.
     
  7. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,996
    2,240
    Nov 15, 2009
    AZ
    First thought is everything is normal for the goofy RVC GM used for these years. The "OMG!!! The alternator quit I am going to walk" volt meter reading is common and normal. Really need a deep cycle battery in these rigs. GM cuts the alternator out to save fuel when the battery is charged and the loads are low. Headlights on bring the voltage up for brighter headlights. Many modes.

    https://noln.net/2017/03/28/battery-management-challenges-smart-system/

    You might need to service the gauge cluster as the swatch gears used are all shot. Known issue for these years.

    Yes, get a real voltmeter or one that plugs into the cigarette lighter that reads volts. (Idiot light style are useless and are sold.) Harbor Freight is good enough. Measure voltage at the battery etc. FORGET ABOUT THROWING PARTS AT IT LIKE ALTERNATORS!!!
     
    jrsavoie likes this.
  8. RobC

    RobC New Member

    7
    8
    Feb 2, 2018
    California
    Thank you War and Smoky. Informative article Wars Thanks...
     
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  9. smokymtn65

    smokymtn65 Active Member

    186
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    Aug 21, 2015
    East TN
    I added one of these usb ports with read out to my '95 crazy how much the gauge changes.
     
  10. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,850
    2,085
    May 9, 2008
    ZEPHYRHILLS FL
    That system was NOT used until the LML IIRC, and even then it was NOTHING like what was used in gassers to satisfy CAFE standards. The only input the ECM or any other controller has on an LLY is to supply the alternator field after the engine has started, and monitor the charge output to turn on the battery light in case of under voltage or no alternator output. So disregard EVERYTHING in regards to the rvc. I don't think GM even used that system on anything but 1500 and down.

    As to the OP, get a voltmeter and see what actual voltage is. Steppers in the cluster often fail in 03-05 trucks. If your voltage was truly that low, I would expect all kinds of alarms from the DIC.
     
    jrsavoie likes this.
  11. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,996
    2,240
    Nov 15, 2009
    AZ
    @THEFERMANATOR o_O Pretty sure a "05 GMC Yukon Denali" the OP is working on is a 1/2 ton and not a diesel. The headlights going on and higher voltage reading is a good clue it has the RVC system.

    It never hurts to test the battery and clean grounds as the system is hard on batteries. However the volt gauge swings are large with the system so again may be normal. That's one gauge GM should have numbed to "idiot light" from the get go.
     
  12. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,850
    2,085
    May 9, 2008
    ZEPHYRHILLS FL
    Oops, I seen 05 and thought lly, but I'm not sure if the rvc system even made it to 6.0l's(most Denali's I've seen have been 6.0l's, but I know some got the l33 5.3l). Last I heard from Ben it was only 4.8/5.3l that got the system. It was only models that fell under the cafe standards that got it. I would have to pull a tune file on one to see if it's enabled or not.
     
    Last edited: Feb 4, 2018
    WarWagon and MrMarty51 like this.
  13. RobC

    RobC New Member

    7
    8
    Feb 2, 2018
    California
     
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  14. RobC

    RobC New Member

    7
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    Feb 2, 2018
    California
    So I put a multimeter on the battery it read 12.3 when I started car it went to 14.4 and when I turned on lights and heater it went to 14.7 so now I'm assuming it's the gauge cluster. Does that make sense or should I check something else ??
     
    MrMarty51 likes this.
  15. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,996
    2,240
    Nov 15, 2009
    AZ
    12.3v is low for a battery being around 70% charged. So you have a bad worn out battery, drain that is discharging the battery, or are not getting it charged up enough. How old is the battery? (Hot weather like Bakersfield means a 2-3 year battery life.) I assume this 12.3v is with only a dome light on? Other higher loads can make the reading off. You want to see 12.6 to 12.8v for a fully charged battery. (Higher is ok if you just charged it.) Charge the battery overnight. Test voltage again. Or have the battery tested. eliminate the battery and it's connections before getting into the charging system.
     
    MrMarty51 likes this.
  16. RobC

    RobC New Member

    7
    8
    Feb 2, 2018
    California
    The 12.3 is with nothing on just battery by itself. The battery is prob 5 yrs old and alternator is fairly new. We live in hot weather (Tracy, CA) but not as hot as Bakersfield I will replace battery and see how the voltmeter on dash does

    Thanks War
     
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