welcome! first you need to find the culprit. is the gas cap tight? if you fix the cause, it goes away on its own after a few drives.
If the problem is minor and it "repairs" itself or the fix is found, it will cancel itself out after a few power cycles. If not, the easiest way is to get an OBD device or some auto parts stores will do it for you for free. But the question still remains, Why is it on?
