Catalytic Converters

The catalytic converter is located in exhaust system in front of the muffler. It is a stainless steel, muffler shaped, device that reduces exhaust emissions by changing toxic gases into less harmful ones.

There are 2 types of catalytic converters: Conventional Oxidation Converters (COC) and Three-Way Converters (TWC). Catalytic converters may be one of 2 designs: a honeycomb-type block which is non-serviceable or small alumina beads that can be removed and replaced on some models.

Even though both converters contain a base material of alumina, COC is impregnated with platinum/palladium and TWC contains material coated with platinum/rhodium. While both converters reduce hydrocarbons (HC) and carbon monoxide (CO), TWC reduces oxides of nitrogen (NOx).

NOTE: Use only unleaded fuel on vehicles equipped with a catalytic converter. If leaded fuel is used, coating of catalytic surfaces will result. If this occurs, converter is useless and must be replaced.

On some models, a TWC is used in conjunction with a COC (fresh air is introduced between converters to aid in oxidation of gases). This is called a dual-bed converter. See Fig 1 .

Fig 1: Cutaway View of Duel-Bed Catalytic Converter

On all other models, first converter (3-way) in exhaust system reduces hydrocarbons (HC) and carbon monoxide (CO), but mainly oxides of nitrogen (NOx). In second converter (oxidation type), with extra air from AIR pump, reduction of hydrocarbons (HC) and carbon monoxide (CO) takes place.