To meet stringent LEV and ULEV emission standards, a considerable amount of development work was necessary to ensure suitable efficiency and durability of catalyst systems. The main challenge is to cut off the engine cold-start emissions. It is known that up to 80% of the total hydrocarbons(THC) emissions are exhausted within the first five minutes in case of US FTP 75 cycle. The problem is that the catalytic converter is not properly operated under 300°C range. The best solution is to use Closed-Coupled Catalyst(CCC) which provides fast light-off temperature by utilizing the energy in the exhaust gas. However, if some malfunction occurred at engine operation and the catalyst temperature exceeds 1050°C, the catalytic converter is deactivated and shows the poor conversion efficiency. 111is paper presents parametric study of engine operating conditions affecting on catalytic converter temperature, which gives catalytic deactivation. Exhaust gas temperature and catalyst temperature were measured as a function of Air/Fuel ratio, Ignition timing and misfire rates. It was found that ignition timing and misfire rates can result in the deactivation of the catalytic converter. Significant reduction in light-off time can be achieved with proper control of the operating conditions, which can reduce cold-start HC emissions as well.