Sierra Denali AWD Stopped working

[JSPA1]

Hi, 

I have a 2002 GMC Sierra Denali that I have owned since new but as of late only drive it on rare occasion. It is bone stock with about 88k miles.  I tried to use it yesterday to do some work around the house and the AWD was not working. The rear axle was spinning but no power to the front axle. This is the full time AWD so no buttons, switches or shifts for the AWD. No grinding, clunking or anything else. Had it not spun pulling  stump i would not have noticed that anything was out of the ordinary. It did occur to me afterwards that i had not noticed it chirping the tires if i turned tight at low speeds like in the driveway as it does when it is working properly. 

 

I checked the 4WD fuse, it was fine, there are no wires off or messed up on the NP149 case that i can see. All is dry and clean. 

 

For grins I have disconnected the battery tonight to see if that helps to reset the ECM, chassis and drivetrain controllers overnight. 

 

Any thoughts on what to do next.