### Catalytic Converter

The catalytic converter is a muffler like container built into the exhaust system to aid in the reduction of exhaust emissions. The catalyst element consists of individual pellets or a honeycomb monolithic substrate coated with a noble metal such as platinum, palladium, rhodium or a combination. When the exhaust gases come into contact with the catalyst, a chemical reaction occurs which will reduce the pollutants into harmless substances like water and carbon dioxide.

There are essentially two types of catalytic converters: an oxidizing type is used on all models before 1980 year. It requires the addition of oxygen to spur the catalyst into reducing the engine's HC and CO emissions into H2O and CO2. Because of this need for oxygen, the Air Injection (air pump) system is used with all these models.

The oxidizing catalytic converter, while effectively reducing HC and CO emissions, does little, if anything in the way of reducing NOx emissions. Thus, the three way catalytic converter.

The three way converter, unlike the oxidizing type, is capable of reducing HC, CO and NOx emissions; all at the same time. In theory, it seems impossible to reduce all three pollutants in one system since the reduction of HC and CO requires the addition of oxygen, while the reduction of NOx calls for the removal of oxygen. In actuality, the three way system really can reduce all three pollutants, but only if the amount of oxygen in the exhaust system is precisely controlled. Due to this precise oxygen control requirement, the three way converter system is used only in cars equipped with an oxygen sensor system.

All models with the three way converter have an oxygen sensor warning light on the dashboard, which illuminates at the first 30,000 mile interval, signaling the need for oxygen sensor replacement. The oxygen sensor is part of the Mixture Ratio Feedback System, described in this section. The Feedback System uses the three way converter as one of its major components.

No regular maintenance is required for the catalytic converter system, except for periodic replacement of the Air Induction System filter (if so equipped). The Air Induction System is described earlier in this Section. Filter replacement procedures are in Section 1. The Air Induction System is used to supply the catalytic converter with fresh air. Oxygen present in the air is used in the oxidation process.