Signs of a Bad Catalytic Converter

When cars were first invented, there wasn’t a ton of thought given to emissions beyond “keep them out of the passenger compartment.” As you can imagine (or if you were around in the ’80s or before, maybe you remember) this wasn’t great for air quality. These days, exhaust systems work to keep emissions to a minimum, and play an integral role in keeping your engine running smoothly. Catalytic converters have come a long way, but they’re still a centerpiece of the system. So what are the signs of a bad catalytic converter? And what should you do if yours has an issue?

One Cool (Scalding Hot) Cat

Catalytic converters take the harmful chemicals that form as a result of the combustion process and render them harmless through chemical reactions at very high temperatures. Traditionally, they live in line with the muffler in the undercarriage, but as technology has advanced, they’re sometimes seen right up on the engine block in one combined unit as a manifold converter. Regardless of where they’re located, catalytic converters contain a honeycomb-like interior composed of materials with chemical profiles that actually change the makeup of exhaust gasses passing through them. They also collect residue and can clog over time.

Some common signs of failure are: Rough performance: If exhaust gasses are having trouble getting through, your intake is also suffering, which means the whole system might not be getting the proper airflow it needs to run smoothly. Back pressure can also cause an engine to stall when driving or not accelerate immediately when the pedal is depressed. Smelly town: It is common to note something like the smell of rotten eggs coming from a bad catalytic converter. This is because unburned fuel contains a sulfate that can build up in a clogged cat, which can lead to that odor. Engine check light/failed emissions test: This is kind of the point of catalytic converters, so there are a number of sensors in place to ensure that the system is working. If it’s not, your car should let you know. Lowered MPG: Connected to poor performance, improper airflow can create an inefficiently rich mixture and leave you burning excess fuel. This further clogs the converter and is wasteful overall. Misfires: Catalytic converters get so hot they can actually ignite unburned fuel inside. This can melt and destroy internal components. Rich fuel causing misfires in the engine creates more blockage in the catalytic converter over time.

No Going Back

Once your catalytic converter fails, there is no fixing it. Replacing the faulty component is the only course of action. They generally last the life of the vehicle, but it’s possible they could fail early. The best way to keep them in good condition is regular vehicle maintenance. Pay special attention to your air-fuel mixture, and don’t forget to clear the undercarriage of your car to stave off rust and contaminants.

A skilled mechanic who notes the above symptoms and is armed with an OBD-II scanner, thermometer and emissions analyzer should be able to make a definitive diagnosis on a failed catalytic converter. At that point, get it changed or you won’t pass inspection or do the environment around you any favors in the meantime.

Check out all the exhaust system parts available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on a bad catalytic converter, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.