Here’s Everything You Need to Know About Catalytic Converters

But what does it do? And how does it work?

Having a properly functioning catalytic converter is required in almost every state to ensure roadworthiness and vehicle registration. They were also big business for thieves for a hot second. But let’s get into what a catalytic converter is, how it works, and why every new car is equipped with at least one.

An engine is an inherently unclean machine. It mixes fuel and air, compresses it, ignites it, and uses the explosion from that ignition thousands of times per minute to propel your car forward. There’s extremely complex chemistry in every combustion, causing harmful raw emissions of carbon compounds, like carbon dioxide (CO2). But there are also other harmful emissions like nitric oxide and nitrogen dioxide, which together form the infamous NOx. 

A catalytic converter almost literally scrubs exhaust gases clean, and in an incredibly interesting way. Formed out of a dense, usually ceramic medium shaped similarly to a honeycomb, there are hundreds of “cells” per square inch that form a dense web of cubes. Onto the ceramic medium, a minuscule layer of precious metals is applied, usually a mixture of platinum, rhodium, and palladium. There are more conventional metals in some converters like cerium, iron, manganese, nickel, and copper. But the active ingredients are the precious metals.

Catalytic converters rely heavily on the heat of the exhaust to work. When cold, they provide almost zero benefits, which is why modern cars have a cold start program that sounds and feels different than normal idle. There are often extra air pumps and extra fuel being injected to light the catalytic converter like a match. Once it hits around 750 degrees Fahrenheit, the converter is up to full operating capacity.

Only then can the dense forest of precious metals can seriously clean up the exhaust gases of any internal combustion engine. The aforementioned gases like CO2 and NOx that come directly out of the combustion chamber get almost scrubbed out of the exhaust gases. According to an article from Harvard University, almost 98% of harmful pollutants from the exhaust are removed. 

The world was much different in 1975. Especially in my native Los Angeles where smog days were a real thing. Folks suffered from poor air quality, developing respiratory diseases like asthma and becoming more prone to respiratory sickness. The emissions from internal combustion engines were posing a health hazard, doubly so in the days of leaded gasoline. 

When the Environmental Protection Agency (EPA) released new regulations for tailpipe emissions, catalytic converters became standard equipment on virtually all cars post-1975. There were few exceptions, with the 1975 Honda Civic CVCC achieving low emissions without a catalytic converter. But after emissions regs tightened even further, Honda couldn’t engineer its way around not having a catalytic converter. 

With almost perfect efficiency at cleaning up harmful gases from the air, catalytic converters are one of the most significant factors of why we have much cleaner air than we did nearly 50 years ago. Some enthusiasts are still under the notion that converters sap performance, but the truth is that modern converters offer virtually zero flow restriction. It’s cleaner and carries a minimal performance penalty. Without converters, our air would be much harder to breathe.

As miraculous as the idea of precious metals making dirty air very clean is, catalytic converters come with a caveat: they have a limited service life and they are costly to replace in modern cars with specialized exhaust routing. Early cars with more universal style piping get much cheaper. They are strictly regulated in some states like California and New York, with mandated materials and longevity to protect consumers from expensive catalytic converter replacements. Other states allow off-the-shelf converters that are less dense and expensive but are less efficient at cleaning exhaust gases.

Generally speaking, catalytic converters should be good for at least 100,000 miles, if not more. Modern onboard computer systems in cars can monitor catalytic converter performance and alert you when it has finally reached the end of its service life. 

There are also other factors that affect the life of a converter. Engines that burn oil tend to destroy catalytic converters, because motor oil coats the miniscule cells of the converter, making it impossible for the gases to make chemical contact with the precious metals. Heat cycling and use also can make or break a converter. Regular long drives that get heat into converters are best for longevity.

A. Yes, very easily. They are expensive but can be purchased online in most states. Used catalytic converters sales are prohibited in California, and California requires a specific, certified converter. As long as you shop for the right one for your car, it should be kosher.

A. Yes. A car will run without a catalytic converter. It won't pass emissions testing without one, though. Therefore, cars that require them aren't considered road-legal without them.

A. Thieves simply cut out the catalytic converter, and your car will be much louder than usual if yours has been stolen. A quick visual test is also a surefire way to tell if someone made off with yours, as a large section of the exhaust system will be missing.