Catalytic Converter 101

What is a catalytic converter and why do they fail? 


Gasoline engines are fueled with two chemical compounds: gasoline and air. Gasoline is made of two basic elements: hydrogen (H2) and carbon (C). In the form of gasoline, these two chemicals combine to make what we call a hydrocarbon (HC). Air is made up of two basic elements: oxygen (02) and nitrogen (N2).


If gasoline engines burned their fuel as efficiently as possible, they would produce three by-products: water vapor (H20), carbon dioxide (C02), nitrogen (N2).


For the most part, these chemical compounds are not harmful but they are not the only gasses in the exhaust emissions.   H20, C02, and N2 are the most desirable by-products of combustion, and automotive engineers strive to create emission control systems that allow a vehicle to produce only these three chemical groups.


Unfortunately, engines don't run perfectly and as a result they also produce three by-products commonly referred to as the "terrible trio" of automotive pollutants. This trio includes the following: carbon monoxide (C0), unburned hydrocarbons (HC), and oxides of nitrogen (NOx).

Carbon monoxide (CO) is an odorless, tasteless, poisonous gas that can cause a variety of health problems, and even death. Many urban areas experience critically high levels of carbon monoxide, especially during the cold winter months when engines take longer to warm up and run cleanly.


With the goal of cleaning the exhaust emissions, all auto manufacturers use catalytic converters on gasoline powered vehicles and since the late 1990’s on diesel powered cars and trucks to eliminate the harmful gasses.


The catalytic converter is a canister (sometimes more than one) that is located in the exhaust system and is filled with a ceramic material that is coated with precious metals that perform a “catalytic” reaction with the exhaust gasses to “convert” them from a pollutant form to a more benign, less polluting, gas.


The state of California has been a leader in requiring the use of catalytic converters since their original designs in the mid 1970’s, and has required all cars sold in the state to conform to very rigid standards that are checked during the bi-annual smog check.  The smog test will determine whether or not your catalytic converter is cleaning the exhaust to the level that has been set for your year, make and model of vehicle.  If the test determines that your car or truck does meet those standards, then all is well and when all fees are paid, you are issued the smog certificate and can register your vehicle for use on the road.  If, however, your vehicle does not pass the smog test, then you will be required to have someone make an evaluation of the problems and correct them before you can re-test the vehicle. 



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