So I have a 2002 LE. Several months ago the check engine light came on, so I ran up to an autozone like auto parts store that a friend works at and had her scan it for me. It came up as a small evaporative leak. She said this is almost always the gas cap being on wrong. So I unscrewed and put the cap back on and she cleared the code. About a month later the light came on. Assuming that I was probably just a dumby and managed to put the cap on wrong again I didn't think anything of it. It eventually went off. Now it goes on and off every so often. I haven't rescanned it yet to see if it's the same code (I don't have the exact code anymore that was originally picked up off the scanner). So here's my question.... Do you guys think that maybe the seal has gone on the gas cap and I just need to replace it? I looked at it and it appears to be fine to me. But what do I know. Gas caps are only $10. Or is there something else actually wrong? I don't have a problem spending the $10 to have it be something else. But I don't really want to trial and error it with different things if I should just take it in. But I also don't want to pay the $70 diagnostic fee for them to tell me to buy a $10 gas cap. Thanks for any help!

Any leak in the evaporative emissions system can cause an evaporative small leak code. A loose, improperly installed or faulty gas cap can certainly cause this code. Another common cause is a sticking evaporative canister vent control valve. There are other things that can cause an evap small leak code as well, including a leaking hose or canister, leaking sending unit seal or gas tank, leaking filler neck, bad purge valve or bad pressure sensor. The only way to be sure is to go through the diagnostic test for the system. The best way is using a "smoke machine" with a scan tool, to force the vent control valve closed and introduce smoke into the system at the evap test port and the smoke can be seen exiting any areas that are leaking. A smoke machine is a several thousand dollar piece of equipment (not including the scantool), so it is typically found in dealerships or well-equipped independant repair shops. A Nissan dealer should also have the tool to test the gas cap as well. So, you can either guess at what the problem is and replace parts, hoping to get lucky, or spend the money to get the system diagnosed so the source of the leak can be properly isolated and repaired.

Thank you! definitely sounds like I better just get it checked out at the dealer.