建議去這裏看看，http://hubpages.com/autos/Catalytic-Converters-For-Dummies
Here is a huge secret that has not made it into the public domain yet:
If you remove a rear oxygen sensor and pack it with red RTV silicone, that will destroy the oxygen sensor in a way that will trick your car's computer into thinking the catalyst is okay. The sensor will not work well enough to report that extra oxygen is coming out of the converter, but it will still generate enough voltage to pass the car's oxygen sensor activity test. Never do this to a front oxygen sensor because it will mess up the fuel system.
其實就是死馬當活馬醫。
一般來說，下遊的o2 sensor 是匯報Cat 狀態的。先拿矽膠蒙上試試，不行再換新的。
盡量不要換cat, 太貴了。
