Check Engine Light Goes On & Off - Gas Cap? Sensor?

Thanks for looking at my question and any help you might offer.

2005 Sunfire. 38000 miles. At 33000 miles the engine light came on, I took it to the dealership, and apparently I just didn't tighten the gas cap enough and that's the reason the light came on. Last week the light came on again, and sure enough, the cap was loose. I drove about 400-500 miles before the light went off. The light came on again today (about 200 miles since it last went off), only this time, the gas cap was tight. I took it to Advance Auto, had them run a scanner on it, they told me my O2 Sensor was bad (Bank 1). I didn't have the $100 with me, so on my way home the light went off again.

Any ideas? Is it common for the light to go on and off when an O2 sensor is going bad? Is it possible I have a leaky gas cap that is messing with the computer and giving false codes?

Again, thanks for any help.
J

it would help greatly to know what code it was. There's a couple dozen different codes that are O2 related, and often the codes are incorrectly assumed to mean the O2 is bad, when its not the case.

There is a very small number of codes that are likely to equal a bad O2, but without knowing the code, I wouldn't assume it.

The reason the light is coming and going is because whatever the failure is, is on the threshold of the parameters. Sometimes it passes the test, sometimes it doesn't.

My Check Engine light went on at 46,000 KM's (from Canada). The dealeship replaced the O2 sensor. Luckily, it was under warranty.

Uncle Bob

I didn't get the code, I just remember them saying something about Bank 1 and upstream, whatever that means.

Thanks.