There isnt a fuse that will just make the check eng light go out. I understand a shop told you to replace the gas cap and that did not work. There is obvouisly a problem somewhere else. A shop would have to do more testing to see what failed; e.I : purge valve, leaky line, bad canister shutoff valve, etc. Another component is at fault if you still have the check engine light on. I would recommend to just ignore the light if your not going to fix the problem.