a redneck.No offense.What do they do,do they tell the pcm I have 02 sensors and there working fine.Why would you get one.Would you pass the scan test and the smog with one.Please fill me in..

 

o2 sims take the power sent by the computer, they turn that power around to match the power that a properly working o2 would send, they do this since a o2 sensor reading exhaust that didnt go through the cat will "red flag" the computer if you will, and the computer i belive goes into "closed loop" so its not using the "broken (or so it thinks" o2 sensor, and then the computer can be happy and think the cats are working fine.

if you wont pass emissions without one, you wont pass with one (unless the only thing holding you back is the ses light or a code that is stored), but if your car is a "gross polluter" now, they wont help that.

now, i have heard some say they help performance by allowing the computer to make better descisions since it is happy knowing the cat is there, but i think the other issue is the ses light.


hope that helps,
james