Everything came within the warranty period, there are slots for O2 sensors, but these stitchings are really very bad. These will surely expire. I don't know if it was these guys first day on the job or if he was a janitor, they also have a welder but those welds are awful week. Probably send back. UPDATE Best part, it doesn't even fit straight, we had to cut it open, screw both expanders to the manifold and weld a piece of pipe in between. Ridiculous for a "straight fit". The thread for sensor 02 is also the wrong size and had to be recut.