The NOx (Nitrogen Oxides) Sensor measures the amount of nitric oxide found in the exhaust system. Besides that, it alerts when the storage limit of these harmful gases is reached. Once the NOx Sensor indicates that the allowable storage levels have been reached, the fuel management system begins the regeneration phase.
The vehicle manufacturer sets the levels of oxides of nitrogen gases that are allowed in the fuel management system. The NOx sensor monitors these levels. If the Engine Control Module (ECM) receives this data from the Oxides of Nitrogen Sensor that is out of range, the DTC P2201 OBD2 will be set.