California catalytic converter
 

Does anyone know if its illegal to add an additional catalytic converter to a car that only has one from factory?

Answer
 

As I understand the emissions law in CA, any change from factory original equipment is a violation.


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Better question is why would you want to?

Just replace the original with a new one.

maybe he has oil slipping past the rings and he want it to test better.

Because I know that the after market cats are not as good as the OE and I don't want to pay 2k for a OE cat. That plus labor will probably be more than my car is worth in kbb.

I see no problem running a couple aftermarket cats....it may or may not provide the effect you are looking for...

Yes, but my primary concern was whether or not it is legal? whunter, said any change in factory original equipment may be illegal, but this is not to alter the original cat, its to add 2 new cats

As long as they are new CARB approved replacements, it should be fine. You certainly can't alter an OE cat or replace one with a used part and be legal, but I have gotten away with it in my state.

Why not call CARB and ask them?

For lots of cars now they send you to a test-only center where a physical inspection is completed (they do this on many of the ~97-2004 models because the OE cats were pretty bad with lots of failures, with the result that lots of people changed them to aftermarket or eliminated them) so any deviation from stock will be noted...assuming the people know what they are looking for.

And while you're not doing anything to the OE cats, you are modifying the factory emission setup...which is why I would suggest asking CARB.

Good luck.

FYI
 

Adding extra units is an alteration.

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aftermarket
 

Is your cat toast. If not what is wrong. Are you not passing smog. An aftermarket cat may work. I know there are Cali legal universal cats from magnaflow. They may have one that fits your car.
Adding more cats would have little effect unless they are close to the engine. They need to be very hot to make the catalyst work. Plus as W.Hunter says its probably not legal.

I have 4 years on my CARB high flow magnaflow cat and I still pass emissions.

Just replace the OE one with a Magnaflow and be done with it. Putting a second on is a waste of time and money.

...except that it's illegal in CA. Magnaflow does make some specific units, but not the inexpensive generic ones.

BTW, it has to meet CARB-II specs now, which means it has to be certified for the year, make, model and engine, thus driving up costs for everyone (while not really doing a thing for clean air...).

Mine was $350 installed if I remember right. They must have a similar unit today. I got mine installed in CA before I moved to Arizona.

I will look into that. I changed my oe cat 2 years ago, but smog is coming up again and the notice says I need to go to a STAR station. I read about STAR and they said its for gross polluters, since I faulted smog in the past. So, I wanted to try to not have the same issue and since my cat is 2 years old (I probably put 80k - 90k miles) on it so I'm kinda leary.