Possible Cause

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.

Malfunctioning EGR valve
Low reading for the EGR valve position sensor
High exhaust temperature
Low coolant level
High coolant temperature
Incorrect coolant/water mixture
Fouled EGR cooler