[Patrick Dickens]

I tapped on the cat with a 2x2 and didn't hear any shaking, rattling or rolling. Should this tell my my cat is ok? And is there a way to check my O2 sensor by looking at it?

[Chopper]

Do you have any reason to suspect your cat is not ok?

[DEWFPO]

If you suspect the cat being bad and if you have one of those laser temp sensors, you could measure the heat of the pipes at the inlet and exhaust of the cat (after completely warmed up and driven of course). You should see a pronounced difference in temp readings. Expecially if the car was just driven.

DEWPFO