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ASVAB · Engine Basics and the Four-Stroke Cycle

What is the purpose of the catalytic converter in a vehicle's exhaust system?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Reduces harmful exhaust emissions by converting carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful gases (CO2, H2O, N2)

  1. A Reduces harmful exhaust emissions by converting carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful gases (CO2, H2O, N2)
  2. B Reduces engine noise
  3. C Improves fuel mileage
  4. D Increases engine power

Why this is the answer

The CATALYTIC CONVERTER uses platinum, palladium, and rhodium catalysts to convert three major pollutants: Carbon Monoxide (CO) → Carbon Dioxide (CO2); Unburned Hydrocarbons (HC) → CO2 + H2O; Nitrogen Oxides (NOx) → Nitrogen (N2) + O2. Required on all US vehicles since 1975. Damage signs: rattling (damaged internal substrate), sulfur/rotten egg smell (running rich), or check engine light (P0420/P0430 codes). Catalytic converters are stolen for the precious metals inside.
Source: ASVAB AI, Emissions Systems

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About this topic: Engine Basics and the Four-Stroke Cycle

Engine basics cover the four-stroke cycle (intake, compression, power, exhaust), the parts that make it happen — pistons, valves, crankshaft, camshaft — and the terms used to describe engines, such as displacement and compression ratio. This is one of 21 Auto Information questions on engine basics and the four-stroke cycle, each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

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