What Are the Signs of a Catalytic Converter Going Out in Your Car?

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A catalytic converter uses a blend of metals to absorb unburned hydrocarbons in gasoline-engine exhaust fumes and reduce pollution. Symptoms of a bad catalytic converter include exhaust noise, drivability issues and odors.

A catalytic converter uses palladium, platinum and rhodium in small amounts to convert unburned hydrocarbons, or gasoline, into substances less harmful to the environment. A catalytic converter works by forcing the exhaust fumes to pass through a tube filled with catalyst material shaped into a honeycomb pattern. The materials in the converter break down the hydrocarbons into carbon dioxide, oxygen, nitrogen and water. As the catalyst is used up or ages, it breaks down and loses volume. This leads to the catalyst breaking into smaller pieces and possibly causing a rattling noise. The exhaust also has two or more sensors upstream and downstream of the converter. These sensors measure the amount of oxygen in the exhaust. The computer interprets these numbers to adjust other engine parameters and check the efficiency of the catalytic converter. If the numbers fall too far outside of the normal range, a check engine light may illuminate in the dash cluster, and the vehicle may start to perform poorly. If the catalyst becomes too small, it can become lodged in the pipe leading toward the back of the vehicle and cause the motor to fail to run. When a catalyst breaks down too far, it can lead to sulfur dioxide emissions and a rotten-egg scent emanating from the tailpipe.