The SCR (Selective Catalytic Reduction) system injects diesel exhaust fluid into the exhaust gases accurately. It increases the temperature of the Diesel Particulate Filter to work efficiently. This process makes the filter have a longer service life and reduces the emissions coming from the exhaust. This entire system is monitored by the PCM or another independent controller that interfaces with the PCM. Regardless, the controller monitors the Oxygen Sensor, Oxides of Nitrogen Sensor, and Exhaust Temperature Sensors to determine the appropriate timing of the reducer information.
If the PCM notices that the Selective Catalytic Reduction System for bank number 1 of the engine is unstable in operation, the P204F OBDII fault code will be set.