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Emission standards are becoming more stringent and at the same time the standards for the On-Board Diagnostic System (OBD) are also continuously enhancing to ensure a more efficient and robust engine emissions monitoring system during the whole vehicle useful life and to improve the quality of the information delivered to the user. In the case of heavy duty diesel vehicles, the Brazilian standards are developed according to the existing European standards (Euro), for example the current standard in Brazil (so called Proconve P7) follows the same requirements of the Euro V with some minor differences. As a consequence, the applied technologies for exhaust gas after-treatment and sensing systems to meet the requirements are already used in European applications such as Selective Catalytic Reduction System (SCR), Exhaust Gas Recirculation (EGR), Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC), as well as temperature, NOx and differential pressure sensors.

Due to the independent operation between the aftertreatment systems and the engine, the aim of the On Board Diagnostic System (OBD) is to ensure the engine emissions stay within the emissions standards during the whole vehicle useful life. In the case of the heavy duty diesel vehicles that use the Selective Catalytic Reduction System (SCR) or the Exhaust Gas Recirculation System (EGR) as the NOx aftertreatment technologies to meet the stringent emissions levels, the use of sensors in the exhaust pipe is required to control and to monitor the engine emissions. These are new and great challenges to the national diesel engine developers who are working with these systems to get the homologation certification. Accurate mathematic models within the automotive control strategies are becoming ever more important and are strongly used to monitor the NOx emissions directly (in case of SCR systems using the NOx sensor) or indirectly (in case of EGR systems using the Lambda sensor).