EGR Valve
WARNING: This page is about a different car, the 2018 Nissan Titan XD. However, it is still accessible from the selected car via links, so may be relevant.
The EGR valve is used by the ECM to control the amount of exhaust gas that flows through the EGR cooler before it enters the intake.
Since the engine does not always need cooled EGR, the cooled EGR flow may be disabled during cold ambient conditions, low speed/load, or if certain DTCs related to the EGR components are current.