Some signs and symptoms that your catalytic converter is clogged are dark colored exhaust smoke, a smell of sulfur or rotten eggs from the exhaust, sluggish engine performance, poor or reduced acceleration and excessive heat under the vehicle.
A catalytic converter that is clogged will block the exhaust gases from going out through the tail pipe properly which creates back pressure on the engine.
So the engine may lose power and you may also notice an increase in fuel consumption as well.
If the catalytic converter is only slightly clogged then using some catalytic converter cleaner can help to unclogged and clean the catalytic converter.
If the catalytic converter is more severely clogged then it will need replaced with a new one.