The other day I turned my a/c on for the first time this year. After about 20 min, the check engine light came on. My husband checked it and it showed an O2 sensor, so he cleared it. The O2 sensor was changed less than 1000 miles ago. Now today, I turned the a/c on again, after about 10 min, the light came back on. The a/c is working great, cold air, car running great, no problems. Any suggestions. The first time this happened the car was sitting idol with the a/c running. Should the code be checked and cleared with the a/c running, because the first time he did it, the a/c was turned off. Thanks for all your help. This is a great site.