My check engine light came on about 40 miles into a new tank of gas. It is a steady light. Per the owner's manual I went through the fuel and refilled. I also put in a can of fuel injector cleaner. The light went out about a 1/4 tank in to the new fuel. However, it came on again after about a week of driving and hasn't gone off anymore. Any ideas before I take it in for testing? Can the gas cap be bad? Thanks

try replaceing the gas cap. they are pretty cheap like 6$ at autozone.

It could be more than the gas that caused the check engine light

check your oil level
tranny fluid (if auto)
brake fluid
all hoses
and anythin ghtat you can really check

In my old 1988 Honda PRelude 2.0S i usta get the check engine light if i was very low on oil. Hope you dont have that problem cause you have been driving with the light on. Not a good thing to do. You shou;d have it checked everytime it comes on.