2008 E250 4.6, 170,000 miles, P0430 code, been getting the code for a while which comes back the first time I drive it after it's cleared. Definitely not an exhaust leak, so it must be down to either catalytic converter or O2 sensor. Is there a way to diagnose it further without replacing parts?

 

You'd want to have a professional-level scanner look at your exhaust system, paying special attention to the O2 sensors operation. The DTC P0430 is a bit too broad to be helpful pin-pointing an exact cause.