Service Engine Light

My service engine light came on and I removed the gas cap and put back on and it remained still lit. So I went by Auto Zone and when they go to put the reader on it the light was off. The man went ahead and put it on and it came back this.....Too much fuel to Bank 2. I called a Chevy dealer and was told that I have a bad oxygen sensor and that I would need to bring it in for them to find which one. Now the question is this...The light has gone off...do I still need to bring it in or is this a minor issue? Any help would be helpful before I approach my husband with the situation. He can be a bear on repairs. Thank you!

oh yes. I forgot to say that my van is a 1997 Astro

I believe if you read you owners manual, it will tell you if the light goes off the condition that cause the light to go on has corrected itself, or does not exsist anymore. But if the light comes on again, obviously some sensor is on it's way out.