4WD not working but no Service 4wd light

Discussion in 'Engine & Drivetrain' started by Dusty_GMT800, Jan 5, 2018.

  1. Dusty_GMT800

    Dusty_GMT800 Full Access Member

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    With the recent snowstorm we had I wanted to take my Tahoe out in the snow, first time with 4wd in weather like this.
    I started the truck, and put it into 4hi after I cleaned the snow off. However, there was no clunk or noise like it usually makes when switching to 4wd. And lo and behold, rear tires spun and the front tires did not move at all
    Truck hasn't thrown a service 4wd light or anything so far, I am thinking it is the transfer case actuator? Since that's what shifts the transfer case and makes the clunking noise I normally hear.
    Is there a way to diagnose the 4wd system that doesn't involve dealerships and big fees?
     
  2. MCAT069

    MCAT069 Full Access Member

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    OnStar can give you codes if there are any stored. Will it shift into 4L? What about neutral?
     
  3. rockola1971

    rockola1971 Full Access Member

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    Are you getting a 4wd indicator light on the dash after "going in 4wd" or are you getting flashing lights on the 4wd panel? Could be stretched transfer case chain to but those usually make noise.
     
  4. Dusty_GMT800

    Dusty_GMT800 Full Access Member

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    I am getting the lights on the switch as well, the switch lights up like normal.
     
  5. Dusty_GMT800

    Dusty_GMT800 Full Access Member

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    Don't have onstar, and it shifts to 4L but doesn't move the front wheels, Haven't tried neutral, how would I know if the truck is in neutral?
     
  6. MCAT069

    MCAT069 Full Access Member

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    Hold 2 WD and 4L down together. The "N" on the shift selector should light up.
     
  7. Dusty_GMT800

    Dusty_GMT800 Full Access Member

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    What would be different so that I'd know I'm in Neutral? The switch lights up for whichever option I select but it doesn't actually go into it, even with 4hi or 4lo lit up it won't actually power the front wheels.
     
  8. MCAT069

    MCAT069 Full Access Member

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    The T case will go into neutral. So, you should be able to hear the actuator moving which would help diagnose the issue. Once the T case is in neutral, the 2 wheel drive light should go off and the "N" should be lit up.
     
  9. rockola1971

    rockola1971 Full Access Member

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    If the dash is showing it went into the selected 4wd range then that tells me the encoder ring within the shift motor is reporting back to the 4wd module (and your dash indicators) that the shift motor went to exactly the position that you commanded at the dash buttons. It sounds like you have either a internal transfer case problem or your problem is up on the front differential (its not locking up solid because of a problem with front axle actuator).
    Have a watch on this vid to troubleshoot which is your problem.
     
  10. Dusty_GMT800

    Dusty_GMT800 Full Access Member

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    So if I don't hear the actuator that would mean it's the problem? I haven't heard the actuator moving at all, the only thing that changes is the light on the switch.
     

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