2000 GMC Sierra 4wd won't shift into 4 hi or AWD

I just started having a problem with my 4wd.
When I push the button to select anything other than 2 hi, the indicator light for the selected range will flash for about 30 sec and then it reverts back to a steady light on the 2 hi button.
I have already replaced the pushbutton unit and nothing changed there.
Can anybody out there help me?
How can I troubleshoot it from this point?
Thanks

I had a simillar problem in my 97 f150. It wouldn't shift into 4wd. I would hit the button and the lights would come on but it wouldn't engage. It was a 5 amp fuse that blue in the fuse box... go figure...

check out the wire harness and plug in on transfer case on passenger side of truck.ive seen several of these just came unplugged or bad connection.its a cream colored accuater that a blue plug harness goes to.

I just started having a problem with my 4wd.
When I push the button to select anything other than 2 hi, the indicator light for the selected range will flash for about 30 sec and then it reverts back to a steady light on the 2 hi button.
I have already replaced the pushbutton unit and nothing changed there.
Can anybody out there help me?
How can I troubleshoot it from this point?
Thanks
Was this fixed? I may be able to help you.

check out the wire harness and plug in on transfer case on passenger side of truck.ive seen several of these just came unplugged or bad connection.its a cream colored accuater that a blue plug harness goes to.
Fishbo, is this in the cab?

on transfer case under truck. passenger side, behind front wheel approx. 2 feet in towards middle of truck

also if i were you i wouldnt use auto 4x4 cause it toasts the clutches in transfer case. ive seen quite a few trucks need new clutches with less than 50,000 miles on them. they should have never had auto 4x4.or had a more quality design.

also if i were you i wouldnt use auto 4x4 cause it toasts the clutches in transfer case. ive seen quite a few trucks need new clutches with less than 50,000 miles on them. they should have never had auto 4x4.or had a more quality design.
Is that even the case with 2005 and above?:confused:

havent heard anything about that. just know 99-02 were bad. everyone that has a 03-newer that i know, i allready told them dont take any chances. i do know the electric connections for transfer case are bad still 03-07 trucks. did you figure yours out yet?

did you figure yours out yet?
Well, I hope so.. I changed the sensor in the encoder motor last weekend. Light has not come on since (service 4wd). But I am still weary though... Fishbo, is the clunk normal when the 4low is engaging? It has always done it since I got it. I just don't know. I am waiting to bump into someone getting in to their GM 4x4 to ask them.
I even changed my u-joint last weekend. It was gone at 36,000. That just doesn't sound right. That was the other clunking I was trying to figure out for a year, until I got on here. A GM mechanic told me that was normal. Man was he wrong! That sound every time I came to a hard stop, stop turn, take off- got on my nerves-:banghead:. 10 dollars for the U (greasable) and 1 hour to change: That was it, and I was purring again.. :loser:

are you putting it in neutral when putting it in 4 low?

are you putting it in neutral when putting it in 4 low?
Yes, and that is the scary part. It has always clunked when you put it in 4Lo. Normal?

Yes, and that is the scary part. It has always clunked when you put it in 4Lo. Normal?

My 02 does that whenever you go from 2-4 but once you get moving she disappears. The clunk is definitely getting worse... my bro says it's time to change out a CV axle.

After a year of messing with it- encoder motors, wiring, ujoints, swapping 4x4 button and trying to fix why it didn't want to go into 4x4 at times (service 4x4 light on at times to), I bought a rebuilt transfer case. Everything is smooth now. Sad to say:frown: is that GM did not want to cover this when my truck had been over three years old (warranty) and under 36,000 (had 27,000 when I took it to GM). I explained that I was deployed for three years on and off and I never seriously thought it was a problem; it was. My transfer case was bad; costing me $1600 this week for the complete fix.