How Do I Test If The Catalytic Converter Is Broken

the only way a cat can be properly checked would be to take it to a garage that can test the co2 emissions. usually if any component of an exhaust becomes blocked the performance of the vehicle will drop off due to back pressure produced in the system. if the blockage is severe enough the engine will simply not start or start then stall quickly afterwards. while i'm no expert, i believe the lambda sensor on the exhaust (whose job is to constantly analise the gasses and send info to the engine management unit so that fuel/air mixture is altered to suit demands) might even cause the unit shut the engine down to prevent damage. it has also been my experience that cats can often collapse inside. if this has happened it would be wise to check the components after the cat as debris can be blown back into the other silencers blocking these too. usually a cat can be expected to last between 50'000 and 80'000 miles depending on driving style and vehicle usage. i hope this info, though limited, goes some way to helping you. good luck.