Originally Posted by
DmaxMaverick
If it has a cat, it won't cause issues removing it. Until DPF came along, they weren't monitored. However, it may not be a cat, but likely a resonator. Look at the intake for an EGR (will be a large valve right in the middle of the manifold inlet). If it has EGR, then it has a cat (and therefore, an S code). Although, I'm not aware of any 2000-ish CA trucks with a GVWR greater than 8600# with any of that. Mine is a 2001 Duramax and doesn't have it. None of the GMT-400, 3500HD should have any smog equipment. The late model 3500HD does, but it's not nearly the same animal (rebadged light truck 1-ton). The 3500HD you have is, in fact, a medium duty truck. In CA, the smog rules never applied to the class until very recently. If, for any reason in CA, an L56 engine was installed in place of the original L65, the law requires that all the smog equipment to follow. I don't know of anyone or company that would abide that, but it is the law, and I'd have no idea why anyone would do that, anyway.