Issues with 4x4

[XtremeTurkey]

I've been having trouble with my 4x4 the passed few weeks and was hoping someone on here could help me narrow down the problem. 1999 GMC Sierra 4.8l

 

My 4x4 quit working and would only stay in 2wd and the service 4wd light would come on when I tried to put it in 4lo. Since then I've replaced the encoder motor with one from the scrap yard, the removed my service 4wd light and now the push buttons work and say it's in 4hi or 4lo but it doesn't actually engage. Would really appreciate help.

[02suburbanZ71]

Dude scan it for codes.

[durandetto]

Can you hear the transfer case engaging? 4lo is pretty noticeable. If so could be an issue with the actuator on the axle.

 

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[00Silverado4x4]

Dude scan it for codes.

This is the best way to find out to avoid throwing parts at it. The parts you replaced from the scrap yard could also be bad as well.

[nick956]

Or lift vehicle on stands and select 4wd either hi or low and see if front wheels spin. If not, and you can hear the encoder motor shift then most likely front actuator that engages the front end.

[kstruckcountry]

Or lift vehicle on stands and select 4wd either hi or low and see if front wheels spin. If not, and you can hear the encoder motor shift then most likely front actuator that engages the front end.

"IFF the driveshaft from the transfer case is turning"

[nick956]

Mmhmm thats right too definitely need that turnin