Description & Operation: Notes

NOTE: Light Duty Emission vehicles are those vehicles whose Gross Vehicle Weight (GVW) does not exceed 8500 lbs.

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

There are three types of catalytic converters: Conventional Oxidation Converter (COC), Three-Way Converter (TWC) and Light Off Converter (LOC). Catalytic converters may be one of 2 designs: honeycomb-type block or small alumina beads.

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

NOTE: Use ONLY unleaded fuel in vehicles using catalytic converters. If leaded fuel is used, the Tetra Ethel Lead will coat the palladium, platinum and rhodium, rendering these catalysts inoperative. If this happens, the converter must be replaced.

On some models, TWC is used in conjunction with 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: Cross Section of Dual-Bed Catalytic Converter (Typical)

On some models, first converter in exhaust system is a LOC. This is a single-bed converter designed to control exhaust emissions during engine warm-up.