Catalytic Converter FAQ

Most questions and concerns regarding aftermarket Catalytic Converters can be clarified by using the helpful California Air Resources Board (CARB) link below:

CARB FAQs – Aftermarket Catalytic Converters.

In addition to CARB’s FAQ, here are some questions that often get asked:

Engine Family Number (EFN)/Test Group Number

Q: How do I find my Engine Family Number or Test Group Number? 

A: ARB describes here where you can find this information or you can click the following link to watch a video that can assist you in locating the emissions control label on your vehicle which would have the EFN noted. Here is a video that shows where the EFN is on an emissions label

Required Documents to determine appropriate Catalytic Converter

Q. What will the Referee need from me to assist in identifying the appropriate CAT for my vehicle?

A: If the are inquiring regarding the need of a replacement CAT, you will likely be asked to provide the Referee with the following:

  • License Plate or VIN number for your vehicle
  • Your Contact information
  • Engine Family Number (EFN) or Test Group Number.
  • Exhaust diagram from the dealer by VIN.
    • Must highlight which converter or converters you are seeking.
    • This needs to come from the dealer by your VIN and not from an online source as every vehicle is different.
  • Picture of the Emissions label.
  • Number of Catalytic Converters that need to be replaced.
  • Verification whether the vehicle requires a rear oxygen sensor.
  • Digital pictures of your exhaust system and catalytic converter locations.
  • You may be required to provide a diagnosis and have a recent failed smog test on record.
    • This does not apply to stolen catalytic converters cases.
    • The diagnosis must identify what part(s) need replacement and be completed by a licensed Smog Test and Repair station.

OBD II and Pre-OBD II Vehicles

Q: Is my vehicle an OBD II or Pre-OBD II?

A: Pre-OBD II vehicles do not stop at 1995 and older. Some Gasoline powered 1996 and newer medium/heavy duty vehicles are OBD I certified (Pre-OBD II) and do not have a rear oxygen sensor. You can look at the Emissions control label (ECL) for information or look at the exhaust system and locate the O2 sensors. We must know whether your vehicle was equipped with a rear oxygen sensor. This sensor is typically after the converter, between the converter and muffler. Sometimes the sensor can be installed into the converter body itself. In the event that the converter is stolen, the thieves often cut the wiring harness and take the sensor. You will want to thoroughly inspect the frame rail and surrounding areas, for any loose wiring. Watch this video for more information.

Here is an image of a 2005 heavy duty vehicle’s ECL that states that the vehicle is OBD I – 

O2 (Oxygen) Sensors

Q: An acceptable aftermarket catalytic converter was installed and I used the correct aftermarket O2 sensor, but I am now getting a check engine light. Will I still be able to pass smog?

A: When installing an aftermarket CAT on your vehicle, we suggest using an OEM (original equipment manufacturer) 02 sensor. Aftermarket 02 sensors have been known to cause check engine lights when used with some aftermarket CATs. If a check engine light is on even after an acceptable aftermarket CAT has been installed, the vehicle will not pass smog.

Q: The check engine light will go away if I relocate the O2 sensor, am I able to relocate the O2 sensor?

A: O2 sensors will need to remain in the same configuration. Relocating the 02 sensor is not acceptable and will be a reason for the vehicle to fail the smog inspection. 

Federal Vehicles

Q: For Federally certified vehicles, can the Smog Referee provide me the exact CAT part number?

A: No. Due to various vehicle configurations and applications, the Referee is not able to provide exact CAT part numbers for Federally certified vehicles. See your local muffler shop for assistance. They have the tools necessary to determine an acceptable replacement.

Q: Federal vehicles are not listed in the California application catalog. How do I determine what catalytic converter to install on a federal vehicle?

A: Find a legal aftermarket catalytic converter for a California vehicle that is of the same make, model, and year as the federal vehicle. The shop will install the California catalytic converter on the federal vehicle, and should note on the invoice and warranty card that the vehicle is a federal model.

Note: Some California and Federal vehicles have a different number of catalytic converters. Please make sure you choose an application appropriate for your vehicle and number of catalytic converters

Exemptions, Warranties and Rescinded Parts

Q. Where can I find the Vehicle and Emissions Warranty periods, including PZEV Models?

A: ARB’s Vehicle and Emission Warranty Periods page has information on PZEV models.

Q. Can aftermarket catalytic converters exempted under the new regulations be used to replace one for my customer’s diesel truck?

A. No. ARB’s regulations for non-OEM aftermarket catalytic converters apply only to gasoline powered vehicles. Similar provisions currently do not exist to allow lower performing non-OEM catalytic converters for use on diesel powered vehicles. Currently, there are no CARB approved Diesel catalytic converters.

Q: Does having a Withdrawn or Rescinded EO Catalytic Converter mean an automatic visual failure?

A: No, having a withdrawn or rescinded EO Catalytic Converter does not mean an automatic visual failure. Review these ET Blast # 35504 and ET Blast # 34105 from BAR for more information.

PC1, PC2, T1 and T2 Configurations

Q: Can I install a PC2 or T2 catalytic converter in a PC1 or T1 application?

A. No, the configuration must match. You cannot install a PC2 or T2 catalytic converter in a PC1 or T1 application. Oxygen sensor must remain in the OEM location. Here is a presentation done by ARB on Aftermarket Catalytic Converters. Slide 7 of this presentation shows PC1 and T1 configuration. Slide 8 shows PC2 and T2 configuration.

If an approved replacement CAT for your vehicle cannot be located and is confirmed unavailable by the Parts Locator Service (PLS), you may be eligible for a Limited Parts Exemption. Refer to our PLS process to learn more.