Truck wont switch back to 2wd

no year car, and matters huge, 1993-2023 up.
they are not ALL the same
no country told
no engine size told or even gas and diesel.
4wd or 2wd, yes low range 4wd.
do not use the 4wd, with 4wd mode set to LOCKED on pavement
not told engine runs. ok, : guess#1 yes
car drives ok in 2wd, in all gears PRNDL, R, D and L????
car fails in 4wd only if yes, say so and tell what 4wd mode it is in
4wd full time 4wc, part time or 4wd lock mode.

sorry we can not guess year,. and 29 long years of evolution on this car, no YEAR told.
AWD called, ALL time 1999, and before that was Select track 1993 first one

did kids play with 4WD levers? seems so to me.
put it 2wd , and learn how to use 4wd later. (ASK),

Check the vacuum switch under the hood in the center of the firewall...follow vac diag

switch on dash can cause this but the transfer case control module is the culprit most times.try disconnecting battery this will should reset the TCM.see what happens.worst case senereo is bad transfer case

sometimes shifting into reverse and backing up a few feet allows the transfer case to shift back to 2wd

if it is a turn knob that puts it in 4x4.then a wire under the truck is touching the exhaust pipe making it do this. I had this happen to mine. It will be 2 wires so they more and likely came loose.

gm has had a lot of problems with the button switch on the dash id start there

There is a vacuum switch on the top of the transfer-case on the driver's side that has gone bad. It's common on out jimmy's and will need to be replaced. Auto Zone or Parts Source will have that part and can give you the step by step instructions to replacing it and take about 15 min to replace. They go for around $25.00 at Auto Zone and $65.00 at the dealers and all you need is a 1 inch open end wrench i believe and patients. It's a tight fit to turn the wrench but you can do it and once loosen, just use your fingers. First disconnect the three vacuum line harness on the vacuum switch and then remove the switch. Once removed, install the new switch and vacuum lines and that's it. Good luck and buy and extra switch and keep it in the glove box. If you push the button for the 2wd, the transfer case will be on the 2wd selection and the front drive shaft will not have any torque to it but the front differential will still be engaged so you can drive it like that till you get a chance to replace the vacuum switch. Good luck and keep warm.

check switch , fuse and relay if good check cable hoses and wiring at transfer are not damaged or disconnected -check actuator for proper movement actuator has a tendency to stick lube actuator rod if necessary

it mabe just the switch sticking
check the connections

Sounds like the shift solenoid