OBD - On Board Diagnose

Exhaust gas recirculation (EGR) plays a central role in the reduction of nitrogen oxides (NOx), which are produced in diesel engines especially under partial load with high excess air. At the expense of fuel consumption and at the cost of increased soot emissions, exhaust gas recirculation replaces part of the fresh air drawn in by exhaust gases. The resulting reduced oxygen content in the cylinder charge ensures a reduction in the nitrogen oxides (NOx) produced during combustion.

Excessive exhaust gas recirculation leads to coking of the intake passages in the medium term. The better way is therefore urea injection SCR into a suitable catalytic converter, which converts the nitrogen oxides into harmless exhaust gas components without the disadvantages of EGR.

See technical article Exhaust gas recirculation (EGR).