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What Are Common Catalytic Converter Problems?

CARS.COM — Catalytic converters are located in the exhaust system between the engine and the muffler, and they are one of the last lines of defense against air pollution from vehicles. They use ceramic-coded beads and various precious metals (the catalysts) to convert pollutants like unburned gas and nitrogen oxide into harmless gases.

Related: Catalytic Converter: What You Need to Know

What Are Potential Issues With a Catalytic Converter?

Catalytic converters often last for 10 years or more, but they can become contaminated, clogged, overheated or physically damaged — leading to sluggish engine performance and, eventually, engine shutdown.

One potential contaminant is leaded gas, which can destroy the catalysts, although it is rarely found in the U.S. Others contaminants include engine coolant, which can leak into the combustion system because of a faulty cylinder head gasket, and engine oil. Those fluids can clog a catalytic converter so that exhaust gases are restricted from passing through. Car engines are like athletes in that they require lots of oxygen. If the exhaust flow is restricted, it means less air can get into the engine and performance suffers. If the engine responds sluggishly or quits after running for a while, a clogged converter could be to blame.

Catalytic converters can overheat because of excessive amounts of unburned gas caused by a misfiring spark plug or a leaky exhaust valve. In addition, a failed oxygen sensor can cause overheating.

On many vehicles, the "cat" is located under the vehicle, and like other parts of the exhaust system, it can also be damaged by road debris or by running over a curb.

Catalytic Converter Theft

Those precious metals we talked about can draw attention: Catalytic converters are frequently stolen because of the precious metals inside. Converters have small amounts of platinum, rhodium and palladium, all of which have value for metal dealers.

Catalytic Converter Maintenance

Among the symptoms of a bad catalytic converter are:

  • Sluggish engine performance
  • Reduced acceleration
  • Dark exhaust smoke
  • The smell of sulfur or rotten eggs from the exhaust
  • Excessive heat under the vehicle

Some of those symptoms can also be caused by other parts of the emissions system, so it's important for a mechanic to diagnose when it's time to replace your catalytic converter.

Following your vehicle's recommended maintenance schedule can help delay this moment as long as possible — often 10 years or more. Keeping your exhaust, emissions and combustion systems in good shape will minimize the risk of your catalytic converter failing before its time.

Finally, don't ignore the check-engine light. Catalytic converter damage is one reason that's one of Cars.com's Top Ten Car Maintenance Crimes. It could be alerting you to a clogged air or fuel filter. Waiting to change that filter could lead prematurely to a $1,000 catalytic converter replacement.

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