For those who may wish to run a catless car and get no codes, or who have a bad cat code thrown [engine light] because the second O2 sensor is not reading differently from the first, here is a fix. There are $80 electronic adapters that go in series with the second O2, but they don't always work and are expensive. So: http://forums.evolutionm.net/1505717-post2.html This is simply using 2 18mm spark plug anti foulers stacked. Then the second O2 is simply screwed in. This lets the sensor 'see' less exhaust, and usually works to stop the code, and maybe get through an emissions test. Am I a horrible polluter and criminal? I have sympathy for those who can not afford $500-$1,400 to get a cat welded in, and need their cars to survive.