What can cause a vehicle’s emissions system to fail?

A faulty catalytic converter can lead to a vehicle's emissions system failing because the catalytic converter is essential for reducing harmful emissions before they exit the exhaust system. Its primary function is to convert toxic gases like carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful substances. When the catalytic converter malfunctions, it can result in increased emissions, triggering a failure during emissions testing.

In contrast, while a malfunctioning fuel pump, an empty fuel tank, or worn-out spark plugs may affect engine performance or fuel efficiency, they do not directly impair the operation of the emissions control system in the same critical way. Therefore, only a faulty catalytic converter directly correlates with failing emissions tests due to its role in pollution control.