Frequently Asked Catalytic Converter Questions

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Catalytic Converters Online knows that people have many questions about catalytic converters and how to install catalytic converters, so we've created the following FAQ resource for our visitors:

Q: Can I use an aftermarket converter to replace a defective converter on my California registered vehicle that has OBD II?

A: Yes, providing the replacement converter has been approved for use on the vehicle by the California Air Resources Board. The converter must be listed for replacement on the specific vehicle and engine size in the manufacturer’s application catalog. It must also have the required markings and E.O. number on the converter body. Current to this information, the following are E.O. numbers issued to AirTek, Inc. from the California Air Resources Board: D-280-73, D-280-77, D-280-79 and D-280-80.

Q: Can a good catalytic converter be removed from a vehicle?

A: No. A good or functioning converter may never be removed from a vehicle. It is a violation that can cost the technician who does so a $2500 fine for each occurrence. Even a Do It Yourselfer, removing one from their own vehicle is subjected to fines.

Q: Can pre-catalysts be removed from a vehicle?

A: No. Pre-cats are treated like any other catalytic converter and should not be removed unless they are defective. Pre-cat elimination converters can only be used when the pre-cat and main converters are bad. They must be approved for this type of use, and should be used in accordance with the aftermarket catalytic converter manufacturer’s instructions.

Q: Can I replace two converters with one aftermarket converter?(example: 1993 Ford F Series Pickup)

A: Yes, but only if the replacement unit has been approved for this and it is used in accordance with the aftermarket converter manufacturer’s instructions.

Q: Can I install dual exhaust or dual catalysts on a vehicle?

A: No. This should not be done unless the vehicle originally came with a dual exhaust or dual catalyst configuration from the vehicle manufacturer. It has been allowed by the EPA, however, to dual an exhaust system behind the existing catalytic converter. If in doubt, it is best to check with the EPA or your local inspection program director.

Q: The vehicle has an engine that is older or newer than the vehicle or a larger engine has been installed. What type of converter, or does a converter need to be installed on this vehicle?

A: The guidelines say that a motor vehicle has to conform to its originally certified engine chassis configuration. If an engine is switched, it must be identical to the original one being replaced. It would be best to consult the local inspection station or EPA before attempting any exhaust system work.

Q: Can I replace a two-way converter with a three-way converter?

A: Yes, provided it has been tested for this type catalyst by the manufacturer in compliance with EPA aftermarket converter procedures.


  • Fill out the warranty card and mail it to the manufacturer.
  • Keep all invoices for six (6) months.
  • Keep all replaced converters for a period of fifteen (15) days. Use the pink copy of the CATCO four-part warranty to tag the converter for easy identification.
  • Follow the CATCO catalog and technical hotline advice.

If in doubt, contact the EPA, your local state inspector or the CATCO technical hotline at (800) 247-2515 for assistance.