Service engine light-Gas tank won't stay pressurized

[Benster]

2004 Nissan Pathfinder LE-104,000 miles

Service Engine light came on a few days ago. My wife had filled it with gas, so I checked to make sure the gas cap was on and "clicked" when I turned it. Not sure if it was on all the way or not, but the light is still on. Ordered a generic gas cap on Amazon, Gates brand, and will try when it arrives. Any other suggestions?

Thanks

[Benster]

Sorry, forgot to add this to original post. Took it to auto parts store and had them read the codes. They said the gas tank was not holding pressure.

[fleurys]

Check your evap lines, but the best would be to run a smoke test on it..you would see it right away...