[BonzoHansen]

As I understand it, the reason is that cats need to reach proper operation temperature ASAP. The further down the pipes the cat moves, the longer it takes to warm up (the air charge cools rapidly). That is what AIR tubes to the cat do (added air makes them hotter).

So in essence by moving the cat(s), you delay cat operation at cold start, and thus increase emissions. (No one moves them closer). If you move it far enough down stream they would never reach proper operating temperature (that is why modern O2 sensors are heated now – constant operating temps). And they can’t test cold start unless you want to drop your car off overnight. Thus, visual inspection.

So, there is some science behind that rule, it is not just a ghey rule meant to personally piss you off. At least that is how it has been described to me.

I don’t really understand the working cat thing, other than just an anti-tampering thing.