Emission regulation by Europe and the U.S. on air pollutants from diesel automobiles which include particulate matter and nitrogen oxides are becoming stricter than ever. The SCR uses Urea, which is NH3 diluted by water, and chemically reacts with emission gases reducing over 90% of the NOx created. In this study several problems were observed in a SCR system and Engine control system. Through this analysis we can find out more effective repair factors from the various fault in SCR component.