A three-way reduction type catalytic converter is used to reduce HC, CO and NOx in the engine's exhaust. The actual catalyst contains Platinum (Pt) and Rhodium (Rh). A few grams of catalyst is applied evenly onto a ceramic honeycomb, which is then installed into a stainless-steel enclosure. The unit is mounted in the exhaust system close to the engine for rapid warm-up to operating temperature.
The function of the catalytic converter is to reduce CO, HC, and NOx by causing these gasses to easily combine with oxygen forming mostly CO2, N2 and water. A very precise amount of exhaust gas oxygen is required for the catalyst to function properly. The ECM reads the oxygen sensor signal and then controls the fuel injection or mixture control solenoid (carbureted vehicles) so there is almost always the exact amount of oxygen required for proper catalyst operation.
A catalytic converter operates at temperatures up to 1500°F (815°C). It can be damaged by prolonged idling, a rich air/fuel ratio or by a constant misfire. Excess fuel will cause the unit to overheat and melt the ceramic substrate. Use of leaded fuel will quickly poison the catalyst and should be avoided. On vehicles sold in the US, catalytic converters are covered by factory warranty for 50,000 miles. However with proper care, on most vehicles a catalytic converter should still be effective for more than 100,000 miles.
- Keep the engine in proper running condition at all times.
- Use only unleaded fuel.
- Avoid prolonged idling. Proper air flow past the catalytic converter is required to prevent overheating.
- Do not disconnect any of the spark plug wires while the engine is running.
- Make engine compression checks as quickly as possible to minimize the fuel pumped into the exhaust system.
If replacement of the catalytic converter or exhaust pipe components is necessary, refer to Engine & Engine Rebuilding of this repair guide for the relevant procedures.