Service 4wd

Discussion in 'Engine & Drivetrain' started by ilmk123, Mar 18, 2018.

  1. ilmk123

    ilmk123 Member

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    Hi everyone.! I am having a problem with my 05 2500 8.1 Suburban. The service 4wd light comes and goes.When it is on the 4wd wont work. Sometimes the lights on the switch go out,change to red and goes in to 4hi or low..Well now recently it started lighting the 4 low light.
    When it does that the tranny shifts like it is in 4 low. It shifts out of 1st really early and shifts out early on the rest also.
    I was wondering if anybody else had seen this before?
    I am thinking encoder...Cause maybe the encoder does not know its location...Or the Tccm for maybe telling it to do so..

    Last night after work the low light was on and i slowed and put the tranny in neutral and it actually went into 4 low..I have checked the fluid and had to add about 1/4 of a quart.
    Any ideas ? Thank you ! Scott
     
  2. Doubeleive

    Doubeleive Elite Member Supporting Member

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    sounds like the dash switch is going goofy, its common, they run around $65 or so last time I did mine. the lights on the switch should not be going out or changing on there own or changing to something different than what you selected, which is a indicator of a bad dash switch. (from my experience) it could always be something else I guess
     
  3. ilmk123

    ilmk123 Member

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    Thanks! I should have said I tried a different switch and still had the service 4wd fault.
     
  4. Doubeleive

    Doubeleive Elite Member Supporting Member

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    well then ya maybe the encoder, I think those run about $195.00 it's a gamble either keep throwing money at it or take it to a transmission shop for a definite check.
     
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  5. Chubbs

    Chubbs Full Access Member

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    If you run some search phrases through Google you will get plenty of hits for the encoder motor.

    A failed encoder motor is famous for engaging a mode other than the last selected when the vehicle was keyed off. There is a YouTube vid for diagnosing the switch with a multimeter but since you have ruled that out already, focus your research on the encoder. You don't need to buy a whole new motor, just the sensor which costs around $40 if I remember correctly. You may or may not need to remove the front driveshaft so that you can get to the motor; it's been done both ways. Remove a few fastneners and you are inside the motor. The tricky part is clocking the gears and syncing the motor back to the Control module. Once again, YouTube tutorials and forum diaries exist for your convenience.

    When I test drove the last truck that I bought, it had the same problems: 'service 4wd' and the buttons wouldn't change modes. Dealer fixed it per agreement and I was told the encoder sensor was at fault.

    Since you had to add TCF I suggest you get back underneath there ASAP and inspect the rear housing for leakage on what looks like a tailshaft. It could be loss of fluid due to a simple output seal but if the oil pump clips are broken off and wore through the output housing then you have bigger problems, if you can believe that. What they call "pump rub" and directly attributable to your app so just something to look out for. Also of note, any tell tale trace of wet fluid there usually originates from the top or upper side of that tailshaft from a pinhole so you have to really get in there, even with a mirror maybe to discover the source if that's what it is.
     
    Last edited: Mar 18, 2018
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