Catalytic Converter & EVAP Systems
Three-way catalytic converter operation, light-off temperature, catalyst damage causes, EVAP system components, charcoal canister, and common EVAP leak codes.
- Explain the purpose of the catalytic converter and what a three-way converter does
- State the minimum light-off temperature for catalyst efficiency
- Identify conditions that can destroy a catalytic converter
- Describe the EVAP system and the role of the charcoal canister
- Recognize common EVAP leak codes and their causes
Lección 1
Catalytic Converter Operation & Light-Off Temperature
Purpose of the Catalytic Converter
The catalytic converter converts harmful emissions (HC, CO, NOx) to less harmful substances. It uses precious metals (platinum, palladium, rhodium) as catalysts to promote chemical reactions that transform toxic exhaust gases into water vapor, carbon dioxide, and nitrogen.
What Is a Three-Way Catalytic Converter?
A three-way catalytic converter reduces HC, CO, and NOx simultaneously. The term "three-way" refers to the three pollutants it handles, not three physical chambers. It performs two types of chemical reactions:
- Oxidation - converts HC (hydrocarbons) and CO (carbon monoxide) to H2O and CO2
- Reduction - converts NOx (nitrogen oxides) to N2 (nitrogen) and O2 (oxygen)
For the three-way converter to work effectively, the engine must operate at or very near the stoichiometric ratio (14.7:1), which is why closed-loop fuel control with oxygen sensors is essential.
Light-Off Temperature
The minimum operating temperature for catalytic converter efficiency is 500-600 degrees F, known as the light-off temperature. Below this temperature, the catalyst is not hot enough to initiate the chemical reactions. This is why most emissions are produced during cold starts before the converter reaches operating temperature.
Exam Tip
Remember 500-600 degrees F as the light-off temperature. Many modern vehicles use close-coupled catalytic converters mounted near the exhaust manifold to reach light-off temperature faster and reduce cold-start emissions.
The catalytic converter converts HC, CO, and NOx into harmless substances. A three-way converter reduces all three simultaneously. The light-off temperature is 500-600 degrees F - the converter does not function effectively below this temperature.