This p-code is pointing to a leak in the EVAP system. The most common fault is a faulty fuel cap. If you have changed the fuel cap, make sure it meets Nissan OEM specs (ie. a cheapy AutoZone fuel cap will not cut the mustard!). Also, fueling the vehicle while it is running will set this code as well. If the fuel cap is tight and correct, then the next best, XXXXX XXXXX way to diagnose this problem is going to be to have the EVAP system "smoked". This is where a machine forces smoke through the EVAP system, and the leak will reveal itself. Most shops charge around $40 for this service, but its money and time well spent. Find it, fix it once, and forget it.