During an inspection, you find that the EGR passages are clogged with carbon buildup. What effect will this have on emissions?

The presence of clogged EGR (Exhaust Gas Recirculation) passages due to carbon buildup significantly impacts emissions, particularly nitrogen oxides (NOx). The primary function of the EGR system is to recirculate a portion of the exhaust gases back into the engine's intake manifold. This process reduces the combustion temperature, which in turn lowers the formation of NOx, a harmful pollutant.

When the EGR passages are obstructed, the flow of exhaust gases back into the intake is restricted. As a result, the engine runs at higher combustion temperatures because it lacks the benefit of the cooler burnt gases that normally dilute the air-fuel mixture. Higher combustion temperatures lead directly to an increase in NOx emissions because these emissions form more readily at elevated temperatures.

Consequently, the obstruction in the EGR system will cause a rise in NOx emissions, making the option indicating increased NOx emissions the correct choice. Understanding this relationship between EGR functionality and emissions is critical for smog repair technicians and highlights the importance of maintaining the EGR system for effective vehicle emissions control.