17 th International Conference on Environmental Science and Technology Athens, Greece, 1 to 4 September 2021 CEST2021_00421 A New Method for Emission Control System Malfunction Detection During the Periodic Technical Inspection REŠETAR M. 1* , PEJIĆ G. 1 , ILINČIĆ P. 2 and LULIĆ Z. 2 1 Centre for Vehicles of Croatia, Capraška 6, Zagreb, HR-10000, Croatia 2 University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Ivana Lučića 5, Zagreb, HR -10002, Croatia *corresponding author: Marko Rešetar e-mail: marko.resetar@cvh.hr Abstract The paper shows a new method for detecting emission control system malfunction during periodic technical inspection (PTI). The on-board diagnostic (OBD) test results were collected and processed during the PTI of vehicles in Croatia in 2020. The study included petrol and diesel passenger cars that passed the tailpipe test and for which an OBD test had also been performed. In 11.5% of the tested cars, at least one stored diagnostic trouble code (DTC) was found. Due to the significant number of vehicles with identified DTCs, a new and more efficient method for the detection of potentially defective vehicles has been suggested. The introduction of the OBD test mandatory for all vehicles equipped with a European on-board diagnostic (EOBD) system is proposed. In addition to the existing OBD data, it is recommended to introduce the number of DTCs as mandatory, and such data should be relevant for passing the roadworthiness test. Keywords: On-board diagnostic (OBD); Diagnostic trouble code (DTC); Periodic technical inspection (PTI); Emission control; Emission standard 1. Introduction Due to the relatively expensive repair and replacement costs of exhaust after-treatment system components, vehicle owners, especially in countries with lower income, often decide to disable their functionality or completely remove them from the vehicle. Although such manipulations are often presented as "not illegal", they conflict with the European regulations' requirements that prohibit the use of defeat devices (Official Journal of the European Union, 2007). Before placing a vehicle on the market, prescribed emission limit values must be met during the type approval emission test. In most cases, in later phases of exploitation, they are no longer monitored. The periodic technical inspection (PTI) of vehicles in Croatia is performed by the Centre for Vehicles of Croatia (CVH) (Rešetar et al., 2018). During the PTI, a tailpipe emission test is compulsory. For diesel vehicles, only the opacity of exhaust gas is measured, and the K- value is calculated. For petrol vehicles, the volume concentration of carbon monoxide is measured, and the lambda value is calculated. Because of limited technical capabilities, existing emission testers in PTI stations cannot be used for the detection of emission control system malfunction. The International Motor Vehicle Inspection Committee (CITA), based on their research, proposed the introduction of emission testing for diesel vehicles involving NOX measurements (CITA, 2019). However, testers that can additionally measure NOX emissions are quite expensive. Equipping all PTI stations, all over the country, with such testers would require significant financial resources and only diesel vehicles would be covered with this new test. According to the European legisla tion, all petrol PCs sold within Europe since 2001, and diesel PCs manufactured from 2004, must be fitted with an on-board diagnostic (OBD) system for emission control (Official Journal of the European Communities, 1998). According to the Directive 2014/45/EU, for roadworthiness tests, the OBD test can be used as an equivalent to standard tailpipe emission testing for Euro 6/VI vehicles (Official Journal of the European Union, 2014). Since 2019, OBD testing methods have been performed in Croatia during the PTI (Rešetar et al., 2019). During the OBD test, the following data relating to the proper operation of the emission control system are collected: malfunction indicator lamp (MIL) status, readiness-code status, number of diagnostic trouble codes (DTCs), and others. The MIL status indicates a malfunction of any emission- related component connected to the OBD system or the OBD system itself. Malfunction means the failure of an emission-related component or system that would result in exceeded emissions. The readiness code is a set of 8 bits, each corresponding to one monitored emissions system in a vehicle. It indicates which of the vehicle’s systems were checked during the diagnostics procedure. The number of DTCs shows the number of faults that the vehicle’s OBD system uses to notify about an issue. When the OBD detects a fault, it will activate the corresponding trouble code. Each code indicates a