The two-speed rear axle shift electrical circuit is inoperative.

Repair the two-speed rear axle shift electrical circuit.

The two-speed rear axle shift actuator is inoperative.

Repair or replace the two-speed rear axle shift actuator. Refer to Two Speed Rear Axle Shift Control Switch Replacement .

There is a lack of air pressure.

Repair the two-speed rear axle air shift circuit.