A vehicle fails a smog check with high NOx emissions. The technician removes the EGR valve and finds no carbon buildup. What should be checked NEXT?

When a vehicle fails a smog check due to high NOx emissions and the EGR valve shows no carbon buildup upon inspection, the next logical step is to check the EGR solenoid.

The EGR (Exhaust Gas Recirculation) system is critical for reducing NOx emissions by recirculating a portion of the exhaust gases back into the intake manifold. This process helps lower combustion temperatures, which in turn reduces the formation of nitrogen oxides. If the EGR valve is clear of carbon buildup, it indicates that the valve itself isn't blocked, but it does not guarantee that the entire system operates correctly.

The EGR solenoid controls the flow of exhaust gases to the intake manifold. If the solenoid is malfunctioning, the EGR valve may not open when it is supposed to, which would prevent the recirculation of exhaust gases and lead to elevated NOx emissions. Checking the solenoid ensures that the system is correctly activating the EGR valve during appropriate engine conditions.

While checking other components such as the oxygen sensor, fuel pressure regulator, or intake manifold can also provide insights into the engine's overall performance, they are less directly related to the operation of the EGR system. The oxygen sensor primarily monitors air-f