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The combustion process creates high volumes of exhaust gases, and they’re riddled with pollutants. For more than four decades, catalytic converters have been used to neutralize the harmful compounds spewed from your tailpipe. On average, a catalytic converter will last for ten years or longer, although environmental and operational issues can cause it to fail prematurely.  

What does a catalytic converter do, exactly, and why could it fail? Here’s what you want to know about its function, what can go wrong, and what it costs to replace this emissions part. 

Lifespan of a Catalytic Converter 

Most catalytic converters eliminate more than 90% of an engine’s harmful emissions. If your vehicle is kept in good working order, it can function well for more than 100,000 miles and sometimes as long as the vehicle is running and driving.  

But catalytic converters aren’t always going to last that long. There can be outside effects that contribute to failures that affect how your engine runs. A poorly operating engine can trash a cat converter in a matter of days, and it’s not a cheap repair to take on.  

What Does a Catalytic Converter Do? 

Did you know your car contains precious metals? Many electronic components contain trace amounts of gold on the contacts, but that’s not what we’re talking about here. The catalytic converter contains rhodium, platinum, and palladium that act as catalyst materials. 

Hot gases from the engine’s combustion process enter the catalytic converter inlet, laden with compounds like hydrocarbons, carbon monoxide, and nitrogen oxides. These gases are responsible for water and air pollution, so it’s important that they’re not spewed into the atmosphere. A ceramic honeycomb-like structure inside the catalytic converter is imbedded with precious metals that react with these gases as they pass through, generating temperatures normally in the range of 1,200 to 1,600 Fahrenheit. The chemical reaction breaks down the compounds into harmless gases including carbon dioxide and water vapor.  

Why it Fails 

A bad catalytic converter rarely just happens due to a manufacturer’s defect. Rather, it’s because of other problems inside and outside of your vehicle. Some examples include:  

  • A misfiring engine. If there’s unburned fuel-air mixture funneling into the converter, it’s going to react with the catalyst materials and can generate ridiculous amounts of heat.  
  • An internal oil leak. If oil consumption is a problem, the catalytic converter could become contaminated and fail.  
  • A cylinder head gasket leak. In a similar way, coolant entering the converter can contaminate the honeycomb. 
  • Impact from the road. The cat converter is mounted under your car in the exhaust system. A big rock or foreign object you drive over could damage the part. 
  • Corrosion. Although the case is corrosion-resistant, it’s possible for a hole to develop in the catalytic converter over time.  

Symptoms of a Failing Cat 

Common Check Engine Light Causes: Catalytic Converter

If your catalytic converter isn’t working properly, you’ll see signs long before you feel any operational difference. Primarily, the Check Engine Light will illuminate with diagnostic trouble codes (DTCs) related to catalyst efficiency – commonly P0420 or P0430. These codes don’t immediately mean a problem with the cat since other issues can cause the DTCs too, like bad oxygen sensors. It’s an early warning sign to pay attention to, though.  

If you need to get a smog check for your car registration, a failing catalytic converter will almost always mean you fail the test. 

A sulfur smell from the exhaust, often identified as smelling like rotten eggs, indicates that the catalytic converter isn’t working efficiently. If the smell persists, there could be a bad cat involved. 

An inefficient or contaminated catalytic converter struggles to burn off the exhaust gases, and temperatures inside can skyrocket. If you see a red-hot glow from under your car, it could be a bad cat overheating. It could be so hot that it starts a fire too. 

If the honeycomb structure inside has deteriorated and begun to break up, you’ll hear a rattle sometimes when the engine is idling and, potentially, on acceleration. It can create an obstruction in the exhaust, putting excessive backpressure on the engine, which could make your engine run rough. Left untreated, it could blow engine oil seals or prevent your car from running at all.  

When to Replace a Catalytic Converter 

If your car has early warning signs of a bad catalytic converter, it might be possible to use a catalytic converter cleaner to decontaminate the honeycomb inside, restoring its function. In many cases, it’s too far gone once symptoms begin. 

If you’ve cleared the DTCs, checked for other causes, and the Check Engine light repeatedly comes on with efficiency codes, it’s a good bet the converter needs to be replaced. As well, a cat will almost always need to be replaced if it has glowed red-hot in the past since the extreme heat will damage the internal structure. The same goes if the honeycomb has already started to break up and there’s a rattle.  

As well, stolen catalytic converters has been a major problem in the US. Obviously, if your catalytic converter has been cut out, you’ll need to have a new one installed. 

What Does a New Catalytic Converter Cost? 

Unfortunately, the part isn’t the least expensive one you’ll find in your vehicle. The cost of a new catalytic converter often ranges from around $100 for a universal fit part to more than $1,200 for a direct-fit component. Most will be somewhere between $300 and $600 for the replacement part alone. As well, you’ll often need new clamps or fasteners, and it’s possible that oxygen sensors will need to be replaced at the same time.  

Labor to change the catalytic converter will also be extra if you choose to have a mechanic take care of the job for you. Since it’s relatively easy to access under the car, $100 to $300 in labor costs will cover it in most vehicles, although there could be extra diagnostic costs or time for related repairs.  

A new catalytic converter is a pricy job but necessary, especially by today’s emissions standards and laws. If you need a new part, help diagnosing the problem, or advice on the repair, an AutoZoner is always willing to assist. Visit a local AutoZone near you for, or check out our list of preferred auto repair shop in your area.

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Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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