98 Silhouette, 187k miles. Check engine light has been on a while. Had it scanned at Autozone, codes P0420 (cat effenciency low-bank 1) and P0172 (fuel too rich-bank 1) showed up. Can this be from a bad 02 sensor or bad cat? Recently, when the the weather got realy cold (for Alabama), in the 30''s,for several days, the light went off, then came back on several days later when the temp was back up in the 40''s.

O2 sensors. I don''t know how many you have though.

A bad O2 sensor iswhat I leaning toward as well. Does anyone else have a comment?

did it get fixed when you changed the O2 sensor?