BTW, these DO NOT throw a code! I thought they did because they have an off road X pipe with no cats, but it turns out that one of the wires on my home made O2 extensions had come loose when I installed it. Now that I fixed it no more engine light!
Obviously every car is different and they might throw a code in your car, but I am just letting you know what is happening with my car. This system comes with 6 O2 bungs. There are 2 on each header collector and 2 on the X pipe. I installed the front O2s on the top collector bungs, the rear O2s on the side mounted O2 collector buns and left the X pipe bungs capped off with the provided caps.