The Exhaust Gas Recirculation System sends a part of the burned gases to the engine induction. Most of the nitrogen oxide is removed there. This system has some built-in sensors. Through these sensors, the PCM (Powertrain Control Module) checks the pressures in the Diesel Particulate Filter (DPF) to reduce soot particles.
Some vehicles have a built-in NOx trap to stop nitrogen oxide particles. They are removed during the regeneration process of the Diesel Particulate Filter. When this system does not work properly, fuel consumption is affected and the DPF ends up blocked.
If the PCM detects pressure levels outside the parameters established by the manufacturer due to excessive NOx accumulation, the EGR system will be deactivated, and the P2BAC OBDII diagnostic code will be set.