I have a 2001 VW Passat. How do I know if the catalytic converter needs to be replaced and also will the engine light come on?
I believe the engine light will come on. There is more than one failure mode for a converter. A common one is a lack of power at higher RPMs. If you are having problems passing someone on the freeway, that is a good chance the converter is almost totally gone.
The engine light will be illuminated.
Who is giving you this “diagnosis” and why is it being suggested?