The switch could be bad, but if you cannot select 4H or 2H, I would think the shift motor in the transfer case is the issue.
This is assuming when you posted "control switch be bad", that you have an ESOF ( Electronic Shift on the Fly ) system.
Some times the Shift motor in the transfer case hangs up, and tapping the back of the transfer case cures the problem. The other thing could be the connector on the transfer case is corroded, remove the connector, and check it for water and other junk, clean if necessary.
You can remove the switch from the dash, and check the resistance on it.
If you secure the truck ( chock the wheels, parking brake, etc ) and having someone turn the ESOF switch from 4L to 2H or 4H, while tapping on the transfer case, this would be a good place to start.
×