2007 2500HD classic won’t go into 4WD and code reader says lost communication with transfer case.

[Dana Floyd]

Hello! Please help! The truck code reader says lost communication with transfer case I replace the switch the little box thingy that is behind the switch the actuator was tested and good cleaned up the ground wire by the driver side door underneath..  still nothing!!!  I am a single broke mom and can’t afford to bring my truck in to the dealership and am at a standstill while it’s snowing by the foot and I’m unable to plow bc I have no 4WD