There are two versions of Transfer cases in 2002. Vehicles built After Jan 2002 may have Electronically Controlled Shift Mechanism. You say "Switched" in your description, so I will assume you have the Electronic version. If your Transfer case difficult to shift or will not shift into desired range. 1) Transfer case electronically controlled shift system malfunction. 2) If vehicle was operated for an extended period in 4HI mode on dry surface, driveline torque load may cause difficulty. Drive the vehicle in a straight line and momentarily release the accelerator. The transfer case can then be shifted to the desired mode. 3) Insufficient or incorrect lubricant. 4) Internal transfer case components binding, worn, or damaged. Other possible causes are; Different Sized Tires; Charging System Diagnostic Codes; Transfer Case Control Module; INTERMITTENT WIRING AND CONNECTORS; Transfer Case Selector Switch; Transfer Case Mode Sensor; Mode Select Circuit open/shorted.