Begin system diagnosis by reviewing the Transfer Case Disassembled View in Transfer Case - NVG 900 Unit Repair, Transfer Case Description and Operation and Rear Drive Axle Description and Operation in Rear Drive Axle. Reviewing the description and operation information will help you determine the correct symptom diagnostic procedure when a malfunction exists. Reviewing the description and operation will also help you determine if the condition described by the customer is normal operation. Refer to Symptoms - Transfer Case to identify the correct procedure for diagnosing the system and to locate the procedure.