In an effort to be a better-informed smog technician I decided to do a little research on the differences between a California legal catalytic converter and a plain ‘ol EPA legal one. Below you will find out what I learned after reading through the current California regulations regarding catalytic converters which went into effect in 2009.

Before I read this lovely piece, I already knew that California catalytic converters were a little more durable than the 49 state ones. An instructor I had in school toured a facility one time that made catalytic converters, and he asked what the difference was. They told him the California one gets dipped twice in the precious metals. But what does that mean in terms of actual longevity?

Well, the California Air Resources Board requires that any aftermarket catalytic converter that is installed in a car that is registered in California must be certified to last for at least 50,000 miles, or five years. They have specific testing requirements that require the manufacturer to certify that the vehicle will pass an emissions test after 50k miles of “typical use.”

(3) Aging of Catalytic Converters for Testing New aftermarket catalytic converters shall be designed by the manufacturer to meet the performance criteria of these procedures for a minimum of 5 years or 50,000 miles. The manufacturer shall demonstrate that the catalytic converter design meets this durability criteria through emission testing conducted after the catalytic converter hasbeen aged to the equivalent of 50,000 miles in accordance with this section.

Then there are OBDII requirements about the cat being able to turn on the light, but when it does turn on the light, the emissions can not be more than 1.5 times the limit of the vehicle for any one gas (we measure HC, CO, and NOx on the dyno test).

1. Incremental Aging of the Catalytic Converter

The manufacturer or independent test facility shall utilize the procedures specified in either Appendix B or Appendix C of these procedures to incrementally age the catalytic converter to the point of MIL illumination on the test vehicle. The catalytic converter(s) aged for MIL illumination demonstration purposes may not be the same converter(s) used for the emission performance evaluation. A catalyst aged to the point of MIL illumination is required for each monitored location in the test vehicle’s exhaust system at which an aftermarket catalytic converter was installed for the emission performance evaluation. Manufacturers may request Executive Officer approval to employ alternate time-and-temperature based methods to age catalytic converters for the purpose of demonstrating compliance with MIL illumination requirements. The Executive Officer shall approve an alternate method if the manufacturer submits data and/or engineering evaluations adequate to demonstrate that the aging process is representative of real world catalytic converter deterioration and/or provides for aging comparable to ARB approved methods.

2. Emission Testing of the Deteriorated Catalytic Converter

After incremental aging of the catalytic converter(s) to the point of MIL illumination, the converter(s) shall be installed on the test vehicle, and the test vehicle shall be FTP emission-tested to determine its emission level with the deteriorated catalytic converter(s) installed. The catalytic converter shall satisfy the requirements for proper MIL illumination if the test vehicle’s emission level does not exceed 1.5 times the OBD tailpipe emissions malfunction criteria to which the test vehicle is certified for any required pollutant (e.g., if the vehicle is certified to an OBD malfunction criteria of 1.75 times the NMOG standard, emissions need to be less than 2.63 (1.5 times 1.75) times the NMOG standard). If the test vehicle’s emission level exceeds 1.5 times the OBD tailpipe emissions malfunction criteria to which the test vehicle is certified (for any required pollutant), the catalytic converter shall be determined to be noncompliant with the requirements for proper MIL illumination.


So a California approved catalytic converter has been proved to last at least 50k miles and still allow the car to pass smog. And beyond that, pollutants can’t be more than 1.5 times the limit of the vehicle with the MIL on. I honestly think that’s quite low since the new federal warranty is 8 years or 80k miles, and California requires PZEV vehicles to be warrantied for 15 years or 150k miles. But there you have it.

So that brings us to the EPA requirements, and how they differ from CARB. According to this document here, and here, the EPA only requires that catalytic converters be warrantied for 25k miles when it comes to emissions testing, and the shell and end pipes must be warrantied for 5 years or 50k miles. It sounds like they have similar testing and recordkeeping requirements as CARB does, it’s just the EPA does not have the same longevity standard as CARB.


I also learned a little about why the state rescinds EO numbers. The state reserves the right to rescind EO numbers when the manufacturer reports more than 100 warranty claims, or 4% of total sales in a given year, whichever is greater.

If, after screening out improper claims, the cumulative number of warranty claims exceed four percent or 100 claims (whichever is greater) for catalytic converters produced for sale in California under any individual Executive Order, the manufacturer shall include in the report a description of the type(s) of failure that have occurred, the probable causes of failure, and data or an engineering evaluation of the impact of the failures on vehicle emissions.

3. For confirmed warranty rates greater than four percent, the Executive Officer may suspend or rescind the Executive Order if it is determined that the catalytic converters are systematically failing in a way that significantly impacts emissions from the vehicles on which they are installed.


And for those of you still with me who are now wondering how I actually tell that a catalytic converter is a California or EPA converter, we must look at the labeling requirements. Below you see a graphic how it looks, sort of. Whenever I peak under the car and I see it’s aftermarket I generally lift the car to read the numbers. I used to try using a mirror but I ended up spending more time reading backwards, it’s just easier to lift the car. I also started doing that because I usually have to mark the converter up with a tire crayon so that I can actually see the numbers. Long story short: the laser markings on the shell don’t last at all and get washed away very quickly. But magically when you melt crayon onto it and wipe it away you can generally make it out. A few manufacturers stamp the shell with the numbers so it makes my job ten times easier. But that’s what I’m looking for when I am verifying a catalytic converter.


And while I’ve never actually seen an EPA catalytic converter, the non-CARB ones I see either have no markings at all or just a random part number, here is what the labeling requirements are for an EPA catalytic converter.


If you guys have any more questions about smogs in California I’m more than glad to try and answer them to the best of my ability.