So the passenger side exhaust manifold on my Xterra cracked, and I popped it off to fix it. In doing so, I had to remove the primary catalytic converter (The damn truck has 4). After I popped it off, I realized the damn thing was hollow! So out of curiosity I also popped the driver side off. Hollow! There’s nothing inside them at all! The best part is, the downstream o2 sensor reads the emissions after this cat, and before the secondary cats. So in theory, the truck should throw a check engine light and a code, but it doesn’t. The OBD2 computer is literally saying all is cool. My truck passed an emissions test like this. I have no idea how, but it did. I also checked for o2 simulators, and there are none. I have no idea what this truck is doing anymore.