Exhaust Exhaust Emissions & Catalytic Converters 1 — Questions and Answers
Question 1: What is the primary function of a catalytic converter in a vehicle's exhaust system?
- To amplify exhaust sound
- To reduce harmful exhaust emissions (Correct answer)
- To increase exhaust flow rate
- To cool exhaust gases
Correct answer: To reduce harmful exhaust emissions
A catalytic converter uses chemical reactions to convert harmful pollutants like CO, NOx, and hydrocarbons into less harmful substances.
Question 2: Which of the following gases is NOT typically targeted for reduction by a three-way catalytic converter?
- Carbon monoxide (CO)
- Nitrogen oxides (NOx)
- Hydrocarbons (HC)
- Carbon dioxide (CO2) (Correct answer)
Correct answer: Carbon dioxide (CO2)
Three-way catalytic converters target CO, NOx, and unburned hydrocarbons; CO2 is a byproduct of complete combustion and is not reduced by the converter.
Question 3: What precious metal is most commonly used in catalytic converters to facilitate oxidation reactions?
- Gold
- Silver
- Platinum (Correct answer)
- Copper
Correct answer: Platinum
Platinum is the primary catalyst used in oxidation reactions within catalytic converters, alongside palladium and rhodium.
Question 4: The OBD-II system monitors catalytic converter efficiency primarily using which sensor?
- MAP sensor
- Downstream oxygen sensor (Correct answer)
- Throttle position sensor
- Coolant temperature sensor
Correct answer: Downstream oxygen sensor
The downstream (post-cat) oxygen sensor compares its readings to the upstream sensor to determine if the catalytic converter is functioning efficiently.
Question 5: Which emission standard, introduced federally in the US, requires vehicles to meet strict NOx and particulate limits?
- Euro 6
- Tier 3 (Correct answer)
- BS6
- CARB LEV II
Correct answer: Tier 3
The EPA's Tier 3 emission standards, phased in from 2017, require significant reductions in NOx and particulate matter from new vehicles sold in the US.
Question 6: What condition is indicated when the Check Engine light triggers code P0420?
- Oxygen sensor failure
- Catalytic converter efficiency below threshold (Correct answer)
- Exhaust manifold leak
- EGR valve stuck open
Correct answer: Catalytic converter efficiency below threshold
OBD-II code P0420 indicates that the catalytic converter's efficiency has dropped below the acceptable threshold monitored by Bank 1.
Exhaust Exhaust Emissions & Catalytic Converters 1
What is the primary function of a catalytic converter in a vehicle's exhaust system?