i just got a 99 Sonoma that i am going to resell. on my way home i took it off road to check it out, and four wheel drive was working fine until i went to disengage it. i hit the 2wd button, but nothing happened. so i turned it off and restarted it and tried again. nothing. i then tried to see if it would go into four low which it did. after that i went to go back into four high, but it skipped right to two wheel drive. now i'm stuck there. no four wheel drive capability at all. is it just something with the buttons or more serious? any help greatly appreciated. thanks, brian

There is a module that controls that basically a sepreate PCM that controls the 4wd it sounds to me like that might be where your problem is check the fuses first both under the hood and in the cab. But It sounds like that module just died out. It is located in the drivers side kick pannel near the floor it's a small rectangular box with 3 plugs into it I belive says 4wd service if you know anyone at a GM Dealer they can check it with the tech 2 to see if that is the problem unfortunately no other scan tools will read it.

Good luck

thankyou very much, i'll check into that. i also heard from a guy at the parts counter at a chevy dealer that it may be the actual switch in the dash. he said they go out a lot on the sonoma/s10 and it's less than $50 to place. very nice. thanks again.

I might have a spare switch and the box laying around let me check my parts. I just parted out a 98 blazer 4wd a couple months back. I can just send you both the little computer box and the switch let me check the garage tomorow and get back to you I know the 4wd worked on the truck I had I checked it so the switch and the box I have are good.