Catalytic Converter: Description and Operation

The Three-way Catalytic Converter (TWC) is an emission control device added to the exhaust system to reduce pollutants from the exhaust gas stream and requires the use of unleaded fuel only.

The three-way catalytic converter coating on the three way (reduction) catalytic converter contains platinum and rhodium which lowers the levels of oxides of Nitrogen (NOx) as well as Hydrocarbons (HC) and carbon monoxide. Also to aid in the conversion process is a base metal added called cerium. Cerium adds the ability of the converter to attract and release oxygen into the exhaust stream. As a catalyst becomes less efficient its capacity to store and release oxygen generally degrades as well. Oxygen storage capability is used as a measure of converter condition, and its ability to perform its function.

The output signal generated by the Heated Oxygen (HO2S) sensor 2 is used to determine the oxygen storage capability of the catalytic converter. Oxygen storage capability is used as a measure of converter condition, and its ability to perform its function. To diagnose the converter the signal from the front sensor must meet certain conditions before reading the rear sensor signal. The front sensor must be switching, indicating a well controlled fuel system. Once the front sensor is determined to be switching, the amplitude of the rear sensor is monitored and a catalyst monitor test is performed.