Hi Mario, I am pleased to assist you. ​Yes, this catalytic converter kit (KIT-111821-2749) is legal for use in California. It complies with both CARB and Federal EPA standards, making it 50-state legal. The kit is compatible with certain 2001–2005 Honda Civic models equipped with 1.7L SOHC engines, but it's essential to confirm the exact year and engine family number of your Honda Civic DX. If your vehicle is compatible with the information provided on our website, use the link below to order while the part is in stock. I hope this helps, and enjoy shopping! https://www.carparts.com/catalytic-converter/walker/kit-111821-2749?cpcid=Q1BHRzQ4NTB8V3JpdHRlbiBJbnRlcmFjdGlvbiBUZWFtIC0gQ1NRQXwvY2F0YWx5dGljLWNvbnZlcnRlci93YWxrZXIva2l0LTExMTgyMS0yNzQ5fDIwMjUwNDE1

It's a 2004 honda civic dx coupe

Hi Mario, I am pleased to assist you. Choosing the correct catalytic converter can be a bit challenging nowadays. It also matters what state you are located in. Check the Vehicle Emission Control Information sticker, usually found underneath the hood, to see if it matches the emission control specifications. Federal emissions (48-state) stickers will simply say, "This vehicle conforms to U.S. EPA regulations," whereas California emissions (50-state, CARB) vehicles will say, "This vehicle conforms to U.S. EPA and the State of California regulations." I suggest calling our parts specialists at 1-866-529-0412 (live agent assistance) during office hours to provide the complete vehicle information and other necessary information so we can help you look for the right part. Have a nice day!