Hello Scotty, Is it possible for a catalytic converter to break down internally without restricting…

Hello Scotty,
Is it possible for a catalytic converter to break down internally without restricting the exhaust? My car won't pass emissions for several reasons, but the mechanic on-site told me the catalytic converter might not be doing its job even though it's not clogged or restricting the exhaust at all. It's a '78 Olds and we suspect the catalytic converter might even be the original one from 1978, so I'm going to be replacing it either way.

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