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4wd not working, testing a 4wd disconnect

Discussion in 'Engine & Drivetrain' started by mntb, Nov 14, 2016.

  1. mntb

    mntb Well-Known Member

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    The 4wd in my tb ext is not working. It stopped working last winter. I'm not entirely certain what the issue is. My normal shop I go to when I can't do something myself charges $90 to read the 4wd code. The light in the instrument cluster is on. The light on the switch all work. I believe I should hear two sounds when switching into 4wd, correct? I only hear one. I'm not sure if it's the disconnect, switch, tccm, or encoder.

    Is replacing the disconnect a pretty straight forward swap?
    If I get a disconnect ($400 new; $100 used), can I simply plug the wiring harness in to test it to see if that's the issue or does it have to be fully installed?
    If the later is true, I will just get the code read first which is what I should do anyway.
    Is $90 about right to read the code?

    Thanks in advance.
     
  2. Matt

    Matt Silver Supporter

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    I'd honestly get the code read first top be 100% sure. If you need a new disconnect, apparently these are very good and are redesigned to eliminate the issues the OEM ones have/had. http://www.ebay.com/itm/161509948512
     
    xavierny25 likes this.
  3. Sparky

    Sparky Moderator

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    One thing you could do to see if it is simply electrical in nature is remove the actuator from the disconnect, then change the mode from 2HI to 4HI and see if the actuator moves or not. If it doesn't, then you may simply have an actuator fault. If it does, then it could be mechanical (or something else).

    You can check mechanical function of the disconnect by jacking up that wheel off the ground and using a screwdriver to push in the hole where the actuator presses while slowly spinning the wheel/axle. If after a short turn the shift fork inside moves and then spinning the wheel makes the front drive shaft spin (or, if 4WD was engaged so the transfer case is locked in and the other front wheel is on the ground you won't be able to spin the wheel anymore), then you know the actuator appears to be mechanically operational. If you cannot get the shift fork to move by pushing it with the screwdriver, or if it moves but never seems to engage, then you know you've got a problem in there.

    Of course, if you have slop where the CV axle connects, then you've got issues in there anyway.

    If all that checks out, then I'd start looking at the encoder motor.
     
    Mooseman likes this.
  4. hockeyman

    hockeyman Silver Supporter

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    Although I think it's mighty expensive, charging $90 sounds normal to pull a 4WD code. The trans shop in my old neighborhood up north wanted $125 to pull the codes from my friends '02 TB.

    Anyhow, *IF* you need to replace the disconnect, here's a good video.


    For some it goes smoothly. For others, well, good luck.
    FYI: Once the disconnect was unbolted, I had one hell of a time getting it to slide off! If I were to do it again, I'd use a Jaw Gear Puller. Couldn't use one at the time because the one I "had" was loaned to a neighbor who hasn't returned it yet...:mad:
     
    xavierny25 likes this.
  5. Mooseman

    Mooseman Moderator

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    And even then, some have had the disco break in the oil pan and then a bitch of a job to get the piece out. If you think you're gonna replace it, start spraying with PB Blaster or other penetrant now. I think the trick is to first turn/twist it in the pan first using a hammer.
     
  6. mntb

    mntb Well-Known Member

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    I read my check engine light read at O'Reilly today. A tccm code C0306- Range actuator control circuit short to ground came up.

    Any idea what this is for? I know it's 4wd related. Hopefully it's what is causing my lack of 4wd and is simple to fix/replace.

    Thanks in advance.
     
  7. Mooseman

    Mooseman Moderator

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  8. mntb

    mntb Well-Known Member

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    Is there different encoder motors for trailblazers or are they all the same and interchangeable?
     
  9. Mooseman

    Mooseman Moderator

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    Only difference is between AWD models (Bravada, Rainier, 9-7x) and real 4x4's (TrailBlazers, Envoys)
     
  10. gmcman

    gmcman Well-Known Member

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    I just had a recent situation similiar to yours, no 4WD and an occasional light on the dash.

    Mine was the transfer case encoder motor, I had A4WD, but no 4HI. The encoder motor would make an engagement noise, but wouldn't engage 4HI. May not be what's going on with yours but here's the thread.

    4WD not working in 4HI | GMTNation
    http://gmtnation.com/forums/threads/4wd-not-working-in-4hi.16212/#post-516923
     
    hockeyman likes this.
  11. smt 59

    smt 59 Well-Known Member

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    Before you start throwing money at this, make sure that you get a for sure assessment, parts and labour get very expensive for these trucks and you don't want to spend $500.00 and find that you still have the same issue when you drive out. These projects snowball as well, I just replaced my disconnect and now found that I have a wobblely C/V shaft as well. Not a big job but you get the idea.
     
    gmcman and hockeyman like this.

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