Description And Operation

DESCRIPTION 

• The Pre-NOx sensor (1/1) is mounted at the elbow of the Diesel Oxidation Catalyst/Diesel Particulate Filter 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.

OPERATION 

• There are two NOx modules and sensors used in the DEF fluid system, upstream and downstream. Both operate similarly to a wide band O2 sensor. The sensors are zirconium-based, multi-layer sensors with oxygen pumps. The NOx modules communicate the amount of NOx to the Powertrain Control Module (PCM) over the J1939 communication bus. The upstream module is located on the right frame rail and the sensor is at the front of the Diesel Particulate Filter (DPF). The upstream module and sensor are used by the PCM to monitor NOx entering the catalyst. By comparing the inlet sensor to the outlet sensor, SCR efficiency can be determined by the PCM.