I can not get my truck to shift into 4wd. It Is an 02 sierra z71 with the electronic shift. I can push either 4hi or 4low and everything seems to work as normal. The light on the button will switch and stay on, I can hear the transfer case switching, and I've even unscrewed the shift motor on the front diff and the actuator is pushing outward. I did have the passenger side axle off of the truck to replace an oil seal, but I've done that before with no problems. I'm not sure where to start at to diagnose the problem. Any Ideas?

Did it quit working after you replaced the axle seal?

I used the 4wd about a week before I replaced the axle seal and didn't need to use it again till a week after. That's when I noticed it wasn't working. I replaced that same seal 2 years ago with out any problems. The only thing that I can think of is that the shift motor is not pushing in all the way.

10 to 1 it's the solenoid on the front axle.
been there !