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EPA Catalytic Converter Info

Important information for professional service providers

Get all the information you need when replacing a catalytic converter for a customer's vehicle. Read on to learn EPA installation requirements, how to determine the Emission Family Number (EFN) and how to find a universal converter.

EPA Installation Requirements

In August 1986, the U.S. Environmental Protection Agency (EPA) issued new proposed guidelines for the construction, efficiency and installation of aftermarket converters. The EPA guidelines state that replacement converters may be installed only in the following situations: 

  • The vehicle is missing a converter

  • A state or local inspection program has determined that the existing converter needs replacement

  • The vehicle is a 1995 or newer model that is more than eight years old or has more than 80,000 miles on it, and a legitimate need for replacement has been established and documented

The service provider must include the customer's name and address; the make, model, year, and mileage of the vehicle on the service invoice; and a stated reason for replacement. When a state or local government has determined that a converter is damaged or needs replacement, the service or repair facility must retain a copy of the written statement or invoice; when a proper state or local government representative has not verified the replacement need, the customer and a representative of the service or repair facility must sign a statement verifying that replacement is justified. 

That statement is printed on the following sheet which is included in every converter carton: 

Furthermore, the EPA has issued the following installation requirements: 

  • The converter be installed in one of the three situations outlined above

  • The converter be installed in the same location as the original converter

  • The converter be the same type as the original converter (i.e., oxidation, three-way or three-way plus oxidation)

  • The converter be the proper one for the vehicle application as determined and specified by the manufacturer

  • The converter be connected properly to any existing air injection components on the vehicle

  • The converter be installed with any other required converter for a particular application

  • The converter be accompanied by a warranty information card to be filled in by the installer

  • Federal law prohibits removal or replacement of properly functioning OE catalytic converters


Engine Family Number

To determine which catalytic converter to use on a vehicle, it is necessary to determine the specific vehicle emission system that was installed by the Original Equipment Manufacturer. This information is included on the Vehicle Emission Control Information (VECI) label required by the United States EPA (see examples below). This label is located in the engine compartment in a visible position on the hood underside, strut tower, radiator support, fan shroud, or firewall.

The label will provide the Engine Family Number (EFN, also known as the Emission Family code or Test Group Number) and other important emission specifications. If the label is missing, it is necessary to contact the OE dealer for the information or to order a new VECI Label. 

How to Find a Universal Converter

As of January 1, 2009, EPA converters cannot be sold or installed in California. Some states like Maine and New York now require use of CARB-compliant aftermarket converters in certain circumstances. It is important to know your state’s requirements to determine the correct converter for your application and location. By law, required CARB-compliant converters must be installed specifically as listed in the Walker catalog, they cannot be substituted nor can they be installed on vehicles that are not listed in the Walker catalog.

As of January 1, 2009, EPA converters cannot be sold or installed in California. By law, required CARB-compliant converters must be installed specifically as listed in the Walker catalog; they cannot be substituted nor can they be installed on vehicles that are not listed in the Walker catalog.

Click here to determine the right aftermarket replacement converter before making your selection.

If you do not find your vehicle listed in the application section of this catalog, you may select a universal converter to repair your vehicle by following the steps outlined below. Universal converters require custom fabrication to fit them into the exhaust system. This type of work requires higher than average skills and is not recommended as a "do it yourself" repair for most consumers. 

Step 1: Determine required body size.

Step 2: Determine the pipe size required.

Step 3: Determine any additional features required such as oxygen sensor fittings, dual inlet pipes, etc.

Step 4: Determine whether a standard converter or ultra EPA-converter is required. Standard converters are recommended for 1995 and older vehicles that are in good working order. Ultra EPA-converters are recommended for OBDII vehicles (1996 and newer models) or non-EGR vehicles with excessive NOx.

Step 5: Choose a converter rated for your engine size. Engine displacements listed for universal converters are the maximum allowed engine size for the converter. The vehicle must have the same size engine or a smaller engine than the engine size listed for the universal converter. 

Step 6: Choose a converter rated for your vehicle weight. Look at the manufacturer's label on the driver's side door pillar to find the vehicle's Gross Vehicle Weight Rating (G.V.W.R.). The vehicle must have the same G.V.W.R. or smaller than the G.V.W.R. listed for the converter.

Step 7: Choose the appropriate converter Type. Vehicles have catalytic converters that operate as either three-way, three-way plus oxidation or oxidation types. Look at the emission label in the engine compartment of the vehicle to determine what type of converter is used. Most universal converters have been designed to work in place of multiple types of catalysts. The chart below shows common abbreviations of catalyst types shown on the vehicle emission label. 

Catalyst Type



Three-Way Plus Oxidation




(Note: All three-way plus oxidation converters will have an air tube, and any converter with an air tube is a three-way plus oxidation converter.)

Learn more about quality exhaust parts, find the right car part, or find a local repair shop today.

The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

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