車上診斷系統（on-board diagnostic, OBD）為針對引擎污染排放之控制系統元件進行監測與診斷是否故障的系統，若有控制元件劣化、故障或不當改裝之狀況，即有可能造成污染物嚴重排放。本論文主要針對使用中車輛污染排放控制系統軟體改裝對污染排放影響進行研究，透過選擇搭載歐規EOBD系統車輛及美規OBD-II車輛各一款型進行污染排放控制系統軟體的一階及二階改裝，再依環保署之”汽油汽車廢氣排放測試方法與程序”於車輛引擎電腦改裝前、後以不同惰轉轉速條件及車速條件等使用惰轉分析儀進行污染排放量測及OBD檢測。從實驗結果顯示不管是歐規車或是美規車，在經過ECU軟體改寫調整後，行駛對應之行車型態時，廢氣中的NOx、THC、NMHC及CO₂排放值皆有增加的趨勢，而CO則是相對減少，但仍符合台灣的排污規範。而在軟體改裝防弊部分則可透過檢視ECU軟體的CVN碼來檢驗ECU軟體是否是原廠版本。本研究成果可做為日後引進使用中車輛實施OBD管制措施時在制度上設計規劃之參考。

On-board diagnostic systems （OBDs）are used for monitoring and diagnosing the functions of engine components to control exhaust emissions. Deterioration, malfunction, or improper installation of emission control components can result in severe exhaust pollution. This paper investigates the emissions of vehicles with emission control software that has been changed to meet both European Union and United States vehicle specifications. We conduct pollution emission tests in accordance with the “Gasoline Vehicle Emission Test Methods and Procedures” of the Environmental Protection Administration on two vehicles with their original electronic control unit （ECU）software and first-stage and second-stage modifications of the ECU software. The test results indicate that the both European and American model cars have a tendency toward higher NOx, THC, NMHC, and CO₂ emissions in the exhaust gas but lower CO emissions after the ECU software rewriting and adjustment. However, all pollution emissions still meet the emission regulations in Taiwan. In the software modification prevention section, we tested whether the ECU software was the original version by examining the Calibration Verification Number of the ECU software. The results of this research can be used as a reference when implementing OBD examinations for in-use vehicles in the future.