4 wheel drive

wow, gee ... try shifting /disengaging in reverse?

Check your transmission fluid level. More than likely it's either low, but since you didn't switch it to 4 low, it's probably a vacuum leak. Remember it should be in neutral to switch back to 2 wheel drive.

you have a lever or switch that engages 2wheel normal driving 4 wheel high for wet slippery conditions ,then you have four wheel low for real muddy and deep snow conditions
normally change from 2 wheel to four wheel high on the move .important nearly all 4 wheel drive vehicles must be stopped to engage low otherwise do damage to transmission

I assume that the vehicle has a rotating knob on the left side of the dash for four wheel drive. It may have been put into 4 low by mistake. To get it out, start the vehicle and put it in drive, select 4 low on the 4 wheel drive selector, take your foot off the brake and get the vehicle rolling at a walking pace (1-2 m.p.h.) then move the selector to 4 high, stop the vehicle and move selector to 2 high.

Be sure to put the truck in neutral, while engine is running, while you disengage from 4 wheel drive (low) to 4 wheel drive (high) and then finally to 2 wheel drive. It is critical to shift transmission into neutral when switching out of 4WD Low, as indicated in your owner's manual. Hopefully, this will help to FixYa problem!

usually the actuator will still make the light still come on if its bad I would check the actuator

If your sure it is acually going into gear than check the auto hubs, they go bad alot. also you can with help from a 2nd person jack the truck up all 4wheels put the truck in 4x4 and drive and see if both drive shafts spin if they do its the hubs if the front one doesnt, its the transfer case

Routinely, you just jack the vehicle enough to have the tires clear the ground and with the engine on, turn full left till it bottoms out....then turn full right till you bottom it out and then repeat up to ten times.....

This sounds like the linkage could have fallen or broken off. Have someone move the 4wd shifter while you look under the vehicle.

My 1999 GMC Jimmy is stuck in 4 low.