I have a 2005 Chevy cobalt LT that has a problem. I've replaced the front o2 sensor three times now in the course of 3 months. The cel keeps coming on saying its giving a bad reading. The catalytic convertor is brand new on it. The dealership replaced it about 7 months ago. What else could've making the o2 sensor go out? Once I replace it, its fine for about a month. Also, cold or wet weather occassionally turns the cel off.