In the article the peculiarities of evaluation the vehicular engine harmful emissions under different heating modes for operation conditions using the heat preparation system of catalytic converter with phase-transitional thermal accumulator are considered. The peculiarity of the heat preparation system is that the thermal energy from different sources of vehicular engine during its working process is accumulated in thermal accumulators. The functional scheme of heat preparation processes of the "vehicular engine - thermal accumulator - catalytic converter" system is shown. The functional scheme takes into account the processes of consumption the fuel, producing the mechanical energy and emission the harmful substances during the vehicular engine operation, which is equipped the exhaust gases cleaning system and heat preparation system with phase-transitional thermal accumulator. The main mathematical dependencies for describing the processes of heat preparation the vehicular engine and the catalytic converter when using the heat preparation system with phase-transitional thermal accumulator are shown. The experimental research results of the catalytic converter temperature condition using the heat preparation system of the vehicular engine under different heating modes are presented. Also the information complex structure for research the impact of the heat preparation system design and regulation parameters on the heat preparation performance of the vehicular engine and exhaust system is shown. The numerical simulation shown, that the fast heat preparation of the catalytic converter to Light-off temperature in exhaust system of passenger car engine without additional heating means is possible only for the moving vehicle. This result is confirmed experimentally. Using the heat preparation system of the vehicular engine catalytic converter can reduce the time of vehicular engine total heating and catalytic converter Light-off point for the 16,7 – 54,5 % and harmful emissions in the processes of after-start heating under operating conditions. This is confirmed by the results of evaluation the vehicular engine fuel consumption and harmful emissions under different heating modes.