I have been researching the exhaust system on my VW Cabrio and have concluded that the smog inspection's most important function is to check for the gases which my VW Cabrio is emitting through the exhaust manifold and then the catalytic converter and ultimately out the tailpipe. So it's obvious the catalytic converter is and should be inspected during the smog check. Since the catalytic converter needs the oxygen sensor to work properly in order to control the reduction of CO, HC, and NO, if the oxygen sensor is not working properly the CAT wont be able to do its job efficiently either.
If the catalytic converter is damaged internally it will more than likely make a rattling noise and if the o2 oxygen sensors fail the check engine light will come on and set a P0420 trouble code which pertain to the catalytic converter; indicating not necessarily the converter being defective but possibly a defective oxygen sensor(s). So my question is how does a smog station which is supposed to check that my VW Cabrio does not pollute only checks the catalytic converter visually and not physically through a catalytic converter efficiency test? There is no way to tell if my VW catalytic converter is bad by looking at it, so why don't smog stations conduct a separate CAT test as part of the smog check? I was told to have my Cabrio's catalytic converter checked but that it is a different service. How can that be if the CAT is such an important part of the emission system?
