Sensor, NOX: Description
WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
The Pre-NOx sensor (1/1) is mounted at the outlet of turbocharger elbow and measures incoming NOx gases. The Post-NOx sensor (1/2) is mounted at the rear outlet of Selective Catalytic Reduction (SCR) Catalyst and measures outgoing NOx gases.