2006 chevy trailblazer_ls
well this actually isn't a question about my TB but since there are some really smart guys here i thought maybe you could help me out. my girlfriend has a 2002 chevy cav. 2.2L. the check engine light comes and goes, so I scanned it and found out the O2 sensor is bad. the thing is, these have a sensor before and after the cat. i'm not sure if the TB's do as well, but anyways, how do I know which one is bad? thanks for your help guys, and hey..at least its a chevy!