What are the signs that a catalyatic converter is going out?

Signs that a catalytic converter is failing include a decrease in engine performance, such as reduced acceleration and power. You may also notice a drop in fuel efficiency and hear unusual noises like rattling from underneath the vehicle. Additionally, the check engine light may illuminate, often accompanied by diagnostic trouble codes related to the exhaust system. Lastly, a strong sulfur smell or exhaust fumes can indicate a problem with the converter.