ok its been bugging the crap out of me i didnt think to look before i had my exhaust put on 2 years ago. Thereare 2 O2 sensors one way up front then a second one. should it be directly in front or directly behind the cat? The guy that did my exhaust put it directly in front and it came up check engine O2 not functional blah blah blah then he moved it to behind the cat cause i toldhim it wasnt working then it came up Catalatic converter not functioning. so i just replaced it with a 15 dolarO2 simulator. but its just been bugging me which one was the proper spot?

 

Behind, from my understanding the second sensors only purpose is to tell the computer that your cat is properly working.Where'd you get your o2 sim at?

 

hmmm...... you should have one O2 right at the Y pipe. and the other one is right after the cat.