This code is triggered when the trans does not shift into 6th gear as instructed by TCM.
Causes: Electrical malfunction (circuits open or shorted) OR mechanical malfunction (control valve sticking, improper solenoid valve operation).
Likely problems, in order of likelihood:
Low fluid level
Shift solenoid mechanical fault
Hydraulic circuit fault
Check fluid level per FSM (available at nissanservicemanual.com), change fluid, and clear codes. It's still relatively new, so I wouldn't suspect a major malfunction yet.