C.A.R.B. or Federal Cats


New Member
Looks like I’m in need of a new set of catalytic converters. It’s a stock 2004 v6 and I live in a state with no emissions testing. I want to keep it fairly stock. It has a California emissions label under the hood. Do I have to get a set that is C.A.R.B. Compliant or can I buy a standard federal set. Is the car tuned for one versus the other?


New Member
Does anybody know if the stock tune is the same for all v6 mustangs? Will a regular set of catalytic converters work on a California emissions car without causing a trouble code to appear?


Profile Violation
NO, they're not the same, but that doesn't matter. They're all 190+ HP (00-04),
regardless of how they get there. You said you live in a state with NO emissions,
so what's the dilemma? I said, if you don't have emissions, get a regular cat, or
not, since there are no emissions... It doesn't matter.


New Member
I guess my dilemma is, will a regular set of cats eventually cause me a trouble code if the car is tuned for California emissions instead of EPA emissions. Just don’t want to spend the money on the regular ones if I’m still going to get an engine light.


Profile Violation
When in doubt, buy the CARB stamped CAT.

Older CA emission cars have another set of pre-cats that the FED emission cars don't have.

CA ECUs have enhanced evaporative emissions capabilities. See the OBDII Theory manual which
can be downloaded for free at www.motorcraftservice.com - specifically the section on the .020
evap testing. They also have mapping for smog pumps, and now with new secondary air injection
systems for PZEV vehicles.

Some vehicles have zero difference between federal and CA emmissions.

Some manufacturers have different blocks, different heads, intake and exhaust manifolds and EGR
systems for the exact same engine, so that one is CA compliant.

Most Subaru's will have a different intake for CA emissions, along with other changes including EGR.

On the Toyota Tundra with a 5.7L and 2 wheel drive the changes are so extensive that CA models have
a different MPG then Federal models. The California models have an extra cat as well as tuning, intake
and other changes.

Some vehicles use different cats (as you indicated).

Some use different tuning.

"CA certified", or whatever, just means that CARB signed off on it too. CARB and
the EPA generally align today, but there can be differences. Back in the day, there
was a huge difference, to the point where many cars had special CA versions because
their regulations were so much stricter, but modern cars are generally 50 state compliant.

Fact of the matter is:
Currently, 16 other states have either adopted, or are in the process of adopting, California's
strict emissions standards. These states include New York, New Jersey, Massachusetts, Maine,
Connecticut, Rhode Island, Pennsylvania, Vermont, New Mexico, Oregon, Washington, Maryland,
Florida, and several others. They vary on when they adopted the standards: Connecticut, for
example, adopted California emissions in 2004, and the strict regulations impacted cars made
in 2008 and beyond. New York agreed to do the same in 2005, and that state required a
reduction in emissions since 2016. When cars are delivered NEW into those states, they
are CA certified emissions cars. My '12 VW is, and it's a PZEV...

California's gasoline also has less sulfur, benzene and hydrocarbons than most gasoline sold
elsewhere in the U.S. so they produce less emissions because the fuel is different. In PA, they
add more ethanol to 10% in the summer blends for lower emissions.

Every car will be equipped with an emissions tag, which will tell you if the vehicle is federal or California
emissions. Federal emissions stickers will just say, "This vehicle conforms to U.S. EPA regulations". California
emissions vehicles will state, "This vehicle conforms to U.S. EPA and State of California regulations".
Others will say "Not legal in California".

There there is difference with California legal and Federal legal emission requirements, and California is stricter.
However, a used vehicle which is equipped with the necessary Federal Emission components is eligible for
California registration as long as the vehicle's exhaust emissions fall within California's limits. It's true, in some
cases Federal cars have different emission components but this does not ban them from being registered in

If it were me, and the CARB cat was available, I would just use it.


New Member
Thanks for the help, and the link. After looking at my set of cats, I was confused about it all. Even with the CA emissions sticker, I don’t have a smog pump but my headers looked as if they had provisions for it but never used. Plus all the converter systems I looked at online had the pre cats on both the CARB compliant ones as well as the Federally regulated ones. This is my first mustang. I bought it for my son to drive when he turns 16, so I’ve had to learn as I go. I do appreciate the help.
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