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4WD issue/not working

Discussion in 'Engine & Drivetrain' started by Daniel644, Jan 8, 2017.

  1. Daniel644

    Daniel644 Well-Known Member

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    So we got hit by several inches of snow Friday night that proceeded to melt all day Saturday only to refreeze to black ice saturday night, so naturally I stayed the F home, today I decided to pull the truck out of the driveway so the rest of the driveway could melt (truck was blocking the sun from hitting it) naturally this took 4WD, so I flip it into 4HI and BOTH 4HI and 4LO are illuminated on the switch, pulling up the driveway feels like 4HI but then as I begin looping the culdesac it feels like 4LO, I shut off and restart the truck and am able to get back to what feels like 2HI, but now I have a Check 4WD light on the IP and ALL the lights on the 4x4 selector are off (they all cycle on and off when cranking), flipping the selector switch around does nothing (including the holding in Neutral position for 10 seconds), truck is an 03 trailblazer with 220k ish miles, transfer case fluid changed when transmission was replaced last year (about this time of year) so about 5-10k miles since last serviced, can't find a fuse for the TCCM like described in other threads here. Advice on where to start?
     
  2. TollKeeper

    TollKeeper Well-Known Member

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    Let the engine idle for about an hour. Let the disconnect get fully warm from the engine warmth. Then disconnect the battery for 10 mins, reconnect and let us know. This has worked for me in the past.
     
  3. Nexus1155

    Nexus1155 Well-Known Member

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    Just bc the tranny was worked on doesn't mean the 4wd disconnect was. Do what he said. If there is still an issue. Definately look at the pass side seal if leaking. If it is. Time to dig deeper and pull off axle and disconnect. Maybe you only have to replace the solenoid on the side of the disconnect?!
     
  4. gmcman

    gmcman Well-Known Member

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    In 4 LO each gear would be good for about 5 mph under normal shifting, would easily be differentiated from 4HI.

    Check the fluid in the transfer case, is the fluid blue in color? Should be GM Autotrac II fluid only, strict 50K change interval. Other fluids may be compatible but not sure what.
     
  5. Sparky

    Sparky Moderator

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    Is the switch original?

    Typically when you get weird stuff going on where the mode light doesn't match the switch setting, the switch is going bad.

    The TCCM fuse isn't labeled TCCM if I remember right.
     
  6. Matt

    Matt Silver Supporter

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    It's fuse #8 in the engine bay fuse box.
     
  7. Daniel644

    Daniel644 Well-Known Member

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    OK, drove to town (it was clear enough to pass on my side of town), parked the car and shut off the engine then turned the key back on and the service 4WD light was out but the selector switch still didn't have anything lit up, removed the key then removed the #8 fuse for about 5 to 10 minutes and the selector was blinking on 2HI so I but the transmission into Neutral and the light went solid, at which point I was able to switch over to A4WD and the light changed then switched to 4HI and it switched (heard the servos both times) then I switched back to A4WD (on my way back to 2HI) and the Service 4WD light came back on and the selector switch went out again.
     
  8. Matt

    Matt Silver Supporter

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  9. Daniel644

    Daniel644 Well-Known Member

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    there was a little bit, but the mechanic said he didn't think that was the issue, he suggested changing the switch on the dash so I did that and still getting Service 4WD lights when I try to drive in 4WD and 1 of the 2 times I tried it since changing the switch I had to pull the #8 fuse to get it to switch back to 2HI, the first time I just had to shut the truck off and switch the key back on, but atleast since changing teh switch a light stays illuminated on the new switch, so I think the old switch was at least part of the problem.
     
  10. Sparky

    Sparky Moderator

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    Another cause of mode selection issues is the encoder motor.
     

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