Glossary
catalytic converter
A catalytic converter is the exhaust part that cleans the exhaust gases. Hot gases pass over a catalyst coated honeycomb that turns carbon monoxide and other pollutants into less harmful ones.
A catalytic converter is the exhaust part that cleans up the gases leaving the engine. The hot exhaust passes through a ceramic honeycomb coated with catalyst metals, and that coating turns carbon monoxide, unburned fuel and nitrogen oxides into carbon dioxide, water vapor and nitrogen.
The catalyst does not get used up; it speeds up the reactions without being consumed. It does need to be hot to work, which is why a car's emissions are worst in the first minutes after a cold start, and why the converter sits close to the engine.
How it is watched is the part worth knowing: an oxygen sensor ahead of the converter and another behind it let the engine computer compare the exhaust before and after, and if the converter stops doing its job the fault is reported through the OBD-II system and lights the check-engine lamp.
Taught in
Related terms
- oxygen sensor — An oxygen sensor sits in the exhaust and measures how much oxygen is left over after the burn, so the computer can tell whether the last mixture ran rich or lean and correct the next one.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)