There's a manual and an electrical method of testing the transfer case shift motor. The manual is simple and quick, while the electrical process is a bit technical. You can manually test the transfer case with the following steps; Firstly, locate the 4WD shifter and carefully remove the knob. From the exposed part, you should see a small hole at the shifter shaft's center. The small pin that controls the shift motor rests in the small hole. Use a screwdriver to push gently and hold the pin down.  If you can, turn the car key to 'on' while holding the pin down. If you can't, get someone to help you turn the car keys to the 'on' position. If the vehicle shifts to the correct gear, the transfer case shift motor works correctly. If the vehicle doesn't respond, you might have to replace the transfer case.