[jcp123]

Cat codes can drive you nuts. I went a bunch of years in my Echo with a bad cat. If I cleared the code during summer on the freeway, it might not come back until I got off the freeway. But if I cleared it at any time during winter, it would come back immediately. If it's a P0420 the cat probably is bad; if it's an O2 code, it deserves more testing (doesn't take long).