I just put in a pde downpipe and when I removed the o2 sensor on the downpipe all the threads came out with the sensor. so I have to buy a new sensor for the downpipe. I called around and I was told by more then one reputable shop that instead of buying a $150 o2 sensor i coulod just plug it up and all that would happen is that i would trip a cel light. i just want to know that running the first o2 sensor is what matter and the second one was just for the cats.