The Engine Control Module (ECM) is responsible for constantly monitoring the various sensors with which the vehicle is equipped to keep the engine running efficiently. It also monitors emissions so that as little as possible is released into the atmosphere.
The ECM uses the NOx Sensor (Nitrogen Oxide) to monitor the levels of this chemical compound inside the exhaust, and thus know the hydrocarbons that will be expelled. Because nitrogen oxide is highly produced in diesel engines, the ECM constantly watches this sensor to make system adjustments accordingly.
When the DTC code P2213 OBD2 is set, it is mostly because a fault was found in the NOx Sensor circuit of bank 2.