There are a variety of electric-shift 
Transfer Cases on the models covered and several different combinations of speed sensors are available. The Vehicle Speed Sensor (VSS) sends information to the PCM for the driveability program and is located at the rear output shaft. The procedure for checking and replacement of the output shaft speed sensor is essentially the same as the procedure for the Vehicle Speed Sensor (VSS). A scan tool must be used to access speed sensor data and trouble codes.