4 wheel drive buttons the light blinks for a while and then switches back into 2WD

with ignition key on push 4wd button and listen under center of truck for a clicking noise. try disconnecting battery and reconnecting it. this will clear tcm memory. get back to us at this post.

the noise you hear under truck tells me your 4wd encoder motor is working but front diff is not actuating. first thing you need to do is when you put it in 4wd slowly move forward and have someone watch front driveshaft to see if it is moving. if it is then we need to look at the front diff, if its not we need to look at transfer case. get baCK TO US