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 emissions control device in the exhaust system, designed to reduce pollutants in the exhaust gas stream, with two types available: 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, so if a malfunction is suspected, it is best to seek diagnosis and repair from a dealer or authorized emissions inspection facility. During any servicing that raises the vehicle, it is important to inspect the converter for leaks, corrosion, dents, and other damage, particularly at the welds and flange bolts connecting it to the exhaust system; any damage found necessitates replacement. While catalytic converters are generally durable, they can become plugged, and a vacuum gauge can be used to check for restrictions. To perform this check, open the throttle to about 2000 rpm, then release it quickly; if there is no restriction, the gauge should drop to no more than 2 in-Hg above its normal reading. If the gauge indicates 5 in-Hg or more above its normal reading or hovers at its highest reading before returning, this suggests that the exhaust system or the converter is plugged, or that an exhaust pipe is bent or dented, or the muffler core has shifted.