Sensor, NOX: 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.