A: A dealer service department should be consulted before replacing a catalytic converter at your own expense because of an extended warranty that the Federal government has mandated. The catalytic converter is a device for controlling emissions which minimizes pollutants in the exhaust stream. There are two kinds of converters available; the conventional oxidation catalyst and three-way catalyst. Diagnosis and repair for this malfunction are best done by taking your vehicle to a dealer or authorized emission inspection facility, since test equipment for a catalytic converter are expensive and sophisticated. When servicing any underbody components, ensure checking the converter for leaks, corrosion, dents or other damage.Pay attention to the welds/flange bolts that attach the front and rear ends of the converter to the exhaust system. If any damage is found then replace the converter. Although rare, catalytic converters do fail sometimes-they can plug off. To check whether a converter is restricted or not, use a vacuum gauge to see how blocked exhaust affects intake vacuum.Connect the vacuum gauge to an intake manifold vacuum source, warm up the engine until it reaches operating temperature, and record vacuum readings at idle and after opening and closing throttle.If reading after fourth test is significantly lower than idle reading, there might be restriction in exhaust system. Spray nuts on the exhaust flange studs before removing them when replacing a catalytic converter. Remove nuts and separate the converter from exhaust manifold then cut off rear portion if necessary. Weld in new gaskets where required.