Rick's Free Auto Repair Advice

Which catalytic converter is best?

Should you buy an OEM catalytic converter or aftermarket catalytic converter?

There’s a HUGE difference in price between an OEM (dealer) and aftermarket catalytic converter so you may be wondering if they’re really different, and if so, how so? The answer is yes, there is a difference. But first, understand that OEM catalytic converters are designed to meet Federal emissions standards for NEW cars, which is 8-years or 80,000 miles. Plus, they’re designed to last the life of the vehicle. So factory OEM catalytic converters have a larger ceramic structure and usually contain more precious metals to ensure they last.

Federal regulations pertaining to aftermarket catalytic converters only require a 25,000 mile warranty. Some aftermarket manufacturers offer longer warranties. However, just like factory converters, the warranty only covers defects in manufacturing.

What isn’t covered by either the factory or aftermarket catalytic converter warranty?

The OEMs and aftermarket manufacturers aren’t stupid. They know perfectly well what causes a converter to fail early. So they exclude damage caused by the follow conditions:

• “Tuning” the PCM with performance software

• Running the engine with non-leaded fuel or adding a high concentration of lead additive to the engine oil. Lead coats the ceramic structure and prevents the catalytic reaction.

• Lack of required maintenance or extended operation with a performance related check engine light. This includes failure to replace spark plugs, ignition wires, faulty ignition coils, sensors, fuel pressure regulator or leaking fuel injectors.

• Damage caused by an internal engine leak of oil or coolant that contaminates the ceramic structure.

• The use of unapproved sealants.

• Extended operation with an improper air/fuel mixture.

• Installation of a catalytic converter on a non-specified year or engine.

Overheated catalytic converter

Overheated catalytic converter

Common catalytic converter buying mistakes

No one is thrilled to shell out $500 to $1,200 for a new catalytic converter, so many DIYers and consumers try to get by with a less expensive “universal” catalytic converter. That’s a big mistake. The converter manufacturers may list a universal converter that fits your vehicle, but they expect that you’ll install it properly the same way as the carmaker. That usually means you have to weld it onto manifold and exhaust pipes. If you don’t do that, the exhaust system can suck in outside air and upset the balance inside the converter.

catalytic converter for Honda

Exhaust manifold catalytic converter

If you try to save money by buying a non-CARB (California Air Resources Board) catalytic converter for use in states that require CARB converters, you’ll waste your money. The converter will fail emissions testing. CARB converters are required in California, New York, and Maine.

Plus, some aftermarket converters simply don’t work well on certain vehicles. They may pass muster in the converter manufacturer’s lab but fail once it’s on the car. Do you have any recourse if that happens to you? Well, maybe. First, you have the burden of proving that your engine is operating properly. Next, you have to request a warranty return authorization from the manufacturer. Finally, you have to return it to them and wait for them to inspect it. If they find any contamination or carbon buildup, they’ll reject your claim. Can you go without driving or passing your state’s emissions while you wait for a refund? I didn’t think so.

Why does an aftermarket converter cause a P0420 or P0430?

Catalytic converters use a combination of precious metals like Platinum Palladium and Rhodium. Each precious metal has its own unique properties. Depending on the price of the metal commodities at the time of manufacture, the aftermarket company may change the recipe, trying to achieve the same results for lower cost.

New catalytic converters leave the factory capable of reducing emissions at 99% efficiency. The efficiency drops to around 95% after about 4,000 miles and then stays at that level for the rest of its useful life. If the efficiency drops to 92% or less, the check engine light will come on. So an aftermarket converter must stay within the 3% range or risk failing the test.

If a carmakers’ testing protocol is particularly rigid, the aftermarket converter may fall outside their acceptable test results, causing an inefficiency code.

So, should you buy an OEM or aftermarket catalytic converter?

I’ve used both and had good and bad luck with aftermarket converters. In cases where the factory converter price is sky high, I’ll take my chances with an aftermarket unit. But in all cases, I make sure I’ve fixed the underlying problem and make sure the driver understands that they must really stay on top of maintenance because, in my experience, aftermarket converters just don’t have the same margin of error as the factory units. If you buy aftermarket, do so with the understanding that it may not work in your vehicle.

For more information on how to diagnose a P0420 or P0430 catalytic converter code, read this

For more information on the proper break in procedure for a new converter, read this

©, 2017 Rick Muscopalt


Posted on by Rick Muscoplat

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