*4lo but no 4hi*

Discussion in 'Transfer Cases' started by rob_z71, Jan 7, 2017.

  1. rob_z71

    rob_z71 Newbie

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    so guys ive been chasing this problem for a while now. truck is a 1998 gmc k1500 with the np1 transfer case. the truck goes into 4lo but will not go into 4hi. when i first bought the truck a few years back it would go into 4hi no problem. as time went on it would only sometimes go into 4hi and now it wont go in at all. it only goes from 2 to 4lo

    things ive replaced (dont worry i returned everything because it didnt fix the problem):
    front diff actuator, transfer case encoder motor, push button on dash, and transfer case control module.

    im at my wits end here and NEED 4hi for the winter. the only things i think are left are the transfer case itself or some sort of wiring problem somehow. i would just swap to a manual floor shift but the money isnt there right now and its much more work. any input would be greatly appreciated, thanks guys
     
  2. Justin S

    Justin S Truck Hoarder

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    Well, it seems like you've narrowed it down to a wiring issue or a transfer case problem.
     
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  3. rob_z71

    rob_z71 Newbie

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    any ideas within those sub categories??? what in the transfer case controls 4hi that doesnt affect 4lo, where do the wires differentiate between 4lo and 4hi, etc. etc. ?????
     
  4. tinfoil_hat

    tinfoil_hat OBS Enthusiast

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    This might be a stupid question but when it goes into 4-lo are you 100% sure you actually have power to the front wheels? The t-case will still shift down to low even if the actuator never engaged. This might make you think that 4-lo works and 4-hi doesn't when in reality neither is working. You can test the actuator by pulling it out of the diff but leaving it plugged in, then hit the button and see if it extends. If not, you narrowed your wiring problem down considerably.
     
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  5. rob_z71

    rob_z71 Newbie

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    I know it goes into 4lo because I've used it in the snow. Recently I've also changed the transfer case switch on top of the transfer case and I still only have 4lo. Another point to add is if I pull the transfer case fuse and/or the 4wd fuse and then put it back in. The truck will go in and out of 4hi for a few minutes until the light for 4hi doesn't even illuminate when pressed just like before but I'll still be able to go from 2 to 4lo
     

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