Well I just put on my header and RK cat but I didnt put the O2 sensor after the Converter back into the piping. I was wondering, since I have no CEL, is this Really gonna affect my car at all because so far I havent noticed anything different without it? I just tucked it up under the car and figured I'd save the $35 the shop wants to install it for me.

You won't pass emmissions inspection. They plug the 'puter into the machine and use sensor readouts to test your system. W/o the downstream sensor, you'll fail. And, no, a 'dummy' rig won't work either. If it don't fluctuate, ya don't pass. Drill a hole where the original O2 sensor was and have a shop weld on an O2 sensor bung over the hole.

yea you need it to pass emmissions. but i had a 99 cavalier sedan the o2 sensor was bolw and didnt work for like a year.i got better fule economey with out it

Well I don't have to worry about emissions checks! I was just curious as to if my car would react negatively to not having this installed in my exhaust.

only the pre-cat o2 sensor is used by the PCM to adjust the mixture. the post-cat sensor is just used to determine catalytic converter efficiency, and will tell you when it's no longer doing its job. soon, im sure your CEL will come on with the "catalyst inefficient" code, or something like that.

yup CEL came on, but I had a shop weld a bung in today. Now I just gotta hope I didnt ruin the sensor the last couple of days because I dont feel like paying $80 for a new one!