Read this thread and check out the TSB.
http://www.clubtitan.org/forums/showthread.php?t=46946I been through this with my 05. I had the p0455 code thrown. Evaporative leak heavy.( Large leak) Nissan says fuel cap for this code. BS. I changed the fuel cap and the code came back. Check the TSB and see if you have the Evap solonoid valve filter installed, If not the valve is crudded up. You have an 04 so your warranty is probably up. What you can do is take the valve out and try cleaning the solonoid shaft inside the valve, it can be seen through one of the ports on the valve. I scraped the crud, blew it out and put a drop of 3in1 oil on the shaft. It lasted for a few months before the code came back. So that told me the valve was bad. I had the TSB performed by Nissan under the extended warranty They installed a new valve and put the filter on. No problems so far.