Due to a Federally mandated extended warranty covering emissions-related components like the catalytic converter, it is advisable to consult a dealer service department before incurring replacement costs. The catalytic converter serves as an emission control device in the exhaust system, designed to reduce pollutants in the exhaust gas stream. There are two types: the conventional oxidation catalyst, which decreases hydrocarbon and carbon monoxide levels, and the three-way catalyst, which also reduces oxides of nitrogen. Testing equipment for catalytic converters is costly and sophisticated; if a malfunction is suspected, it is best to visit an authorized emissions inspection facility for diagnosis and repair. When servicing underbody components, inspect the converter for leaks, corrosion, dents, and other damage, including checking the welds and flange bolts connecting the converter to the exhaust system. Although failures are rare, catalytic converters can become plugged. To check for a restricted converter, use a vacuum gauge while opening the throttle at around 2000 rpm and then releasing it quickly. A properly functioning system will show a quick drop in gauge reading to no more than 2 in-Hg above its normal level. If the gauge indicates 5 in-Hg or more above its normal reading, or hovers at a high reading before returning, it suggests that the exhaust system or converter is plugged, or that there may be a bend or dent in the exhaust pipe, or a shift in the muffler core.