The Engine Control Module (ECM) monitors every one of the various sensors with which the vehicle is equipped to keep the engine efficient and functional. Also, it constantly monitors emissions and ensures that the least amount of hydrocarbons are expelled into the atmosphere.
The ECM uses Nitrogen Oxide (NOx) Sensors to monitor the levels of nitrogen oxide found in the exhaust and to know which hydrocarbons are being expelled. The DTC P2217 OBDII code setting indicates that the Nox Sensor circuit voltage is not within the range determined by the manufacturer.