When testing catalytic converter efficiency, what reading indicates a failure of the catalytic converter?

A high reading of NOx emissions in the exhaust indicates a failure of the catalytic converter because it suggests that the converter is unable to effectively reduce nitrogen oxides (NOx), which are harmful pollutants produced during combustion. The primary function of a catalytic converter is to convert these harmful emissions into less damaging substances before they are released into the atmosphere.

When a catalytic converter is functioning correctly, it significantly reduces NOx emissions, along with hydrocarbons (HC) and carbon monoxide (CO). If NOx levels remain high despite being within the operational parameters, it indicates that the catalytic converter is either damaged, failing, or clogged, thereby impairing its ability to carry out its essential role in the exhaust system. This reading is critical for determining not only the performance of the catalytic converter but also the overall emissions performance of the vehicle in question.