What is the result of an air injection failure on exhaust gases?

An air injection system is designed to introduce additional air into the exhaust stream, primarily to facilitate the oxidation of unburned hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases. This process helps reduce the emissions of these harmful substances by promoting complete combustion in the catalytic converter or during the exhaust phase.

When there is a failure in the air injection system, the supplemental air is not introduced into the exhaust flow. As a result, the unburned hydrocarbons that would normally be oxidized in the presence of air remain in the exhaust, leading to an increase in hydrocarbon emissions. Therefore, the correct answer accurately captures the consequence of an air injection failure: a noticeable increase in hydrocarbon levels in the exhaust gases.

In contrast, other gases are affected differently. A failure may not necessarily cause a large increase in carbon monoxide itself, nor would it result in moderate decreases in carbon dioxide or oxygen levels in a way that is directly linked to the air injection system’s function. Carbon dioxide would typically remain stable unless there are more comprehensive combustion issues, and while oxygen levels might decrease slightly due to incomplete combustion, the primary and most direct effect observed is the increase in hydrocarbons.