Is there a common problem or something that I may be overlooking?

I have a 2004 h2 with about 250,000 miles. Great condition, always taken care of when problems arise but this time I am not sure about dealership after the last time I took it there. So now, the front end is " locked" like it is in 4x4 high or low.
I noticed that the front end diff doesn't have a actuator like the trucks that are 4 wheel drive, so I'm assuming they are different because the hummer is awd.

I did unplug the actuator on the transfer case and will try it tomorrow but I noticed that I have an error now telling me to check the 4 wheel drive. I'm not too sure if it will even help but I wanted to try things this time before even considering the dealership.

Thanks for the help!