I have a 2008 Cobalt with a 2.2 litre engine, automatic transmission. Vehicle has 45K miles, and about 95% of driving is on the Interstate @ 70 MPH. About once a month, the "Check Engine" lite comes on for about 2-3 days, then will go out. Spits out a code P2271, HO2S Signal Stuck Rich Bank 1 Sensor 2. Before I take this to the repair shop, does anyone have any ideas what might be causing this code? The car runs great, and performance/fuel mileage do not seem to be affected. Like I said before, it's very intermittent, AND seems to occur shortly after refueling. I do not try to squeeze more fuel in after the gas pump clicks off, (I know that's a no-no), not so sure that my GF doesn't try to overfill. I've told her not to, but ?????. Any thoughts are appreciated! One last thing, is Sensor 2 the "Downstream" O2 sensor? Thanks!