Catalytic Converter Legality Checker
Some states require a CARB compliant converter and will fail an EPA one at inspection. Check what your state and vehicle need before you buy.
Your vehicle and state
- Emissions rules change. Confirm current requirements with your state before purchasing.
- A CARB compliant converter is legal in all fifty states. A federal EPA one is not legal in CARB states.
- Converters must be matched to the specific vehicle, engine and emissions family, not just to pipe diameter.
This is general guidance, not legal advice. Emissions regulations differ by state and change over time. Confirm current requirements with your state's regulator or an authorised inspection station before buying. Tampering with emissions equipment on a road vehicle carries federal penalties.
Two standards, not one
Aftermarket catalytic converters are built to one of two standards. Federal EPA converters meet the national requirement. CARB converters meet California's stricter standard and carry an Executive Order number stamped into the body.
California, New York, Colorado and Maine require the CARB standard. An EPA converter fitted in those states will fail inspection even if the car runs perfectly and the tailpipe numbers are fine. Everywhere else, EPA is acceptable and CARB units are legal too.
Fix the cause before fitting the part
Catalytic converters very rarely fail on their own. They are poisoned or overheated by something upstream: a misfire dumping raw fuel into them, an engine burning oil or coolant, a leaking injector, or a failed oxygen sensor causing a rich condition.
Fit a new converter without finding that cause and the new one dies the same way, usually inside a year and usually outside whatever warranty came with it.
P0420 does not always mean the converter
On an OBD-II vehicle, P0420 means the computer decided the downstream oxygen sensor is tracking the upstream one too closely, which suggests the converter is not doing its job. An exhaust leak, a lazy sensor or a fuel trim problem produces the same code. Diagnose it before buying anything.
Frequently asked questions
Which states require CARB compliant catalytic converters?
California, New York, Colorado and Maine. In those states a federal EPA converter will fail inspection. Requirements do change, so confirm with your state before buying.
What is the difference between CARB and EPA converters?
CARB converters meet California's stricter conversion efficiency and durability standards and carry an Executive Order number stamped on the body. They contain more precious metal and cost noticeably more. A CARB converter is legal in all fifty states, an EPA one is not.
Will an aftermarket converter set a check engine light?
It can. Aftermarket converters sometimes cannot convert quite as efficiently as the original, and the downstream oxygen sensor sees the difference, which sets P0420. Buying the grade specified for your vehicle's emissions family rather than a generic universal unit reduces the risk substantially.
Can I just remove my catalytic converter?
No. Removing or defeating emissions equipment on a road registered vehicle is a federal offence in the United States, and selling or installing defeat devices carries significant penalties. It will also fail any emissions inspection and set a permanent fault code.
Everything on this page is an estimate worked out from the numbers you entered and typical figures for the conditions you picked. Your vehicle, your parts and your conditions will differ. Check anything you intend to act on against the manufacturer's specification, the service manual, or a qualified technician. Verifying the result before relying on it is up to you.