Symptoms of a Bad or Failing Catalytic Converter

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A catalytic converter is a car component that works to reduce vehicle emissions and pollution. It is a metal canister installed in the exhaust system. It is filled with a chemical catalyst, usually a platinum and palladium mixture, and helps to convert the vehicle’s emissions into non-harmful gasses. Usually, a faulty catalytic converter will produce one of 5 symptoms that alert the driver that replacement may be required.

1. Reduced Engine Performance

One of the first symptoms commonly associated with a bad or failing catalytic converter is a reduction in engine performance. The catalytic converter is built into the vehicle’s exhaust system, and as a result, can affect the performance of the engine if it develops any problems. A clogged converter will restrict exhaust flow, while a cracked one will leak harmful gas. Either fault can negatively affect engine performance and cause a reduction in power and acceleration as well as fuel economy.

2. Rattling Noise

Rattling noises from under the vehicle are another symptom of a bad or failing catalytic converter. If a catalytic converter becomes old or damaged internally from excessively rich fuel mixtures, the catalyst coated honeycomb meshes on the inside of the converter can collapse or break apart, causing a rattle. The rattle may be more obvious when starting the vehicle and will worsen over time.

2. Sulfur Smell from Exhaust

During engine combustion, sulfur-containing gasoline becomes hydrogen sulfide. A properly working catalytic converter will convert hydrogen sulfide into odorless sulfur dioxide. When failing, you may notice a sulfuric, rotten egg-like smell coming from the exhaust. Unburnt fuel left in the exhaust by the bad catalytic converter produces the odor, and may even cause dark exhaust smoke.

4. Check Engine Light Comes On

A bad or failing catalytic converter can also cause an illuminated Check Engine Light. The oxygen sensor and air-fuel ratio sensor in modern vehicles monitor the efficiency of the catalytic converter by tracking the gas levels in the exhaust. If the computer detects that the catalytic converter is not operating correctly, or not catalyzing the exhaust gases properly, it will set off the Check Engine Light to alert the driver of the problem. A variety of other issues can activate the Check Engine Light, so it is recommended to have the vehicle scanned for trouble codes to be certain of the issue.

5. Failed Emissions Test

Some states in the U.S. require a diagnostic check of the engine’s computer to pass an emissions test. A trouble code will be stored in the car’s computer if it has a faulty catalytic converter. Should this pop up, the car will fail the test.

The catalytic converter is one of the most important emissions components found in modern vehicles. Without it, the vehicle may produce excessive emissions harmful to both humans and the environment. If you suspect that your catalytic converter may be having a problem, have the vehicle inspected by a professional technician to determine if the car will need a catalytic converter replacement.


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Joel

19 years of experience
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Joel
19 years of experience
Acura RL - Check Engine Light is on - Jacksonville, Florida
very knowledgeable and precise. able to fix electrical issues in my car. Right on time for the appointment.
Toyota Highlander - Check Engine Light is on - Jacksonville, Florida
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31 years of experience
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Matthew
31 years of experience
Jeep Patriot - Check Engine Light is on - Norfolk, Virginia
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14 years of experience
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Michael
14 years of experience
Ford Mustang - Check Engine Light is on - Decatur, Georgia
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Michael arrived on time and was efficient. He also explained the issues my car was having in an understandable way, and gave me good advice on what to do moving forward with the repairs.

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15 years of experience
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Christopher
15 years of experience
Honda Accord - Check Engine Light is on - Fairburn, Georgia
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