Are Cold Air Intakes Illegal? What Drivers Need to Know in 2025

Generally, a cold air intake is not inherently illegal, but its street legality depends on where you live and whether the specific kit is certified to meet emissions and noise rules. In California and other states that follow California’s standards, a cold air intake typically needs a CARB Executive Order (EO) number to be legal on public roads; under U.S. federal law, any intake that increases emissions or defeats emissions controls is prohibited. The same “legal if compliant” principle applies in Canada, the UK/EU, Australia, and elsewhere.

What a Cold Air Intake Is—and Why Its Legality Varies

A cold air intake replaces or re-routes the factory airbox and ducting to draw cooler, denser air. While that can marginally improve throttle response or power, it can also alter how the engine management system measures airflow. If a kit causes higher emissions, trips a check-engine light, or increases intake noise beyond legal limits, authorities can deem it unlawful for street use. Certification requirements and enforcement differ by jurisdiction.

United States: Federal Rules and State-by-State Nuance

Federal law (applies nationwide)

The U.S. Clean Air Act prohibits “tampering” with emissions controls. An aftermarket intake is legal to install and use on public roads only if it does not increase emissions or disable/defeat emissions systems. Many reputable manufacturers design “emissions-legal” intakes that maintain proper sensor operation and do not raise emissions. Marketing language such as “for competition/off-road use only” means a part is not legal for public roads, regardless of where it’s sold.

California and CARB-adopting states

California requires most emissions-related aftermarket parts, including cold air intakes, to carry a CARB Executive Order (EO) number to be legal for on-road use. The EO certifies the part does not reduce the effectiveness of emissions controls. Many other jurisdictions that follow California standards treat CARB-EO parts as legal for street use. As of 2025, states with California-style programs include, among others, CA, CO, CT, DE, ME, MD, MA, MN, NV, NJ, NM, NY, OR, PA, RI, VT, VA, WA, plus the District of Columbia. Local enforcement details vary, but California performs visual inspections; inspectors typically look for the EO sticker/plate on the intake.

Inspections and real-world enforcement

Even outside California, inspections commonly check for check-engine lights and OBD-II readiness. An intake that causes lean codes, MAF sensor issues, or requires a non-compliant tune can trigger a fail. Some areas also enforce noise rules; while exhaust noise gets most attention, excessive induction noise can draw scrutiny where external noise limits apply.

Outside the U.S.: The Same Principle—Compliance First

Canada

Under federal law and provincial regulations, it is unlawful to tamper with emissions controls or increase emissions. Many provinces no longer run routine emissions tests for light-duty vehicles, but the legal obligation remains: an intake must not degrade emissions or safety. Enforcement can occur during roadside checks or inspections following a complaint or collision.

European Union and United Kingdom

Vehicles must retain type-approval compliance. In practice, that means the intake should be homologated or accompanied by a recognized certification (for example, TÜV/ABE in Germany). In the UK, an intake is generally legal if the car still meets emissions and noise limits and passes the MOT; insurers must be notified of the modification. Police can issue a defect notice or prohibition if noise or emissions standards are breached.

Australia and New Zealand

Modifications must comply with Australian Design Rules (ADRs) and state/territory codes. Intakes that increase induction noise or impact emissions can be deemed illegal without certification or engineering approval. Some states require inspection and a modification plate/certificate for certain intake changes. New Zealand operates similarly under LVVTA rules for modified vehicles.

How to Tell if a Specific Cold Air Intake Is Street-Legal

Use the following checks to determine if the intake you’re considering—or already installed—is legal for public-road use in your area.

• Look for certification: In California/CARB states, verify a CARB Executive Order (EO) number for your exact vehicle year/engine. Keep the EO label installed for inspections.
• Confirm manufacturer claims: “50-state legal” generally means a CARB EO exists; “49-state legal” excludes California/CARB jurisdictions. “Off-road/competition only” is not street-legal.
• Check local inspection rules: Ask a licensed inspection station whether visual checks apply and whether an intake without an EO can pass in your state or province.
• Verify emissions readiness: After installation, confirm no check-engine light, no pending codes, and all OBD-II readiness monitors are set.
• Assess noise: If the intake uses an open cone or resonator delete, ensure the vehicle still meets applicable noise limits.
• Keep documentation: Save purchase records, EO printouts, and installation instructions; bring them to inspections.
• Retain the stock parts: If a test or roadside check is looming, having the OEM airbox makes reverting straightforward.

Working through these steps greatly reduces the risk of an inspection failure or a roadside citation, and it helps you avoid buying a part that isn’t legal for your region.

Common Myths and Facts

Misconceptions about intakes can be costly. Here are frequent claims and the reality behind them.

• “All cold air intakes are illegal.” False. Many are street-legal when properly certified and installed.
• “If it passes OBD, it’s legal everywhere.” Not always. Some jurisdictions require visual verification or specific certifications (e.g., CARB EO).
• “No tune = automatically legal.” Not necessarily. An intake can still alter emissions or trigger faults without a tune; conversely, some tunes make a setup illegal even if the intake is fine.
• “‘Off-road only’ is just a disclaimer.” It’s a legal warning. Using such parts on public roads can result in fines and failed inspections.
• “Noise laws only cover exhausts.” Many places regulate total vehicle noise; loud induction can be cited.

Understanding the difference between marketing claims and regulatory requirements helps ensure your modification complies with the law.

Practical Risks: Insurance, Warranty, and Reliability

Insurers in many countries (notably the UK and Australia) require disclosure of performance modifications; nondisclosure can jeopardize coverage. In the U.S., the Magnuson-Moss Warranty Act prevents blanket warranty voids, but a dealer can deny coverage for failures caused by a modification. From a reliability standpoint, poorly designed or oiled filters can contaminate MAF sensors, leading to drivability issues and inspection failures.

Bottom Line

A cold air intake is not automatically illegal. In the U.S., it must not increase emissions under federal law; in California and CARB-aligned states, it generally needs a CARB EO to be street-legal. Elsewhere, legality hinges on maintaining emissions and noise compliance and, in some cases, having recognized certification. Check local rules, verify certifications, and keep documentation to stay on the right side of the law.

Summary

Cold air intakes are legal in many regions when they’re certified and do not compromise emissions or noise standards. In California and CARB states, look for a CARB EO number; across the U.S., ensure no emissions tampering. In Canada, the UK/EU, Australia, and New Zealand, the same principle applies: modifications are permitted if they maintain compliance and—in some cases—carry appropriate approvals. Always verify your exact kit’s status for your vehicle and jurisdiction before installing or using it on public roads.

Can a cold air intake throw a code?

So, can a cold air intake cause a lean code? Well, it is a possibility. However, it’s usually not the intake itself but installation errors or related components.

Is a cold air intake legal in CA?

No, most aftermarket cold air intakes are not legal for street use in California because they lack a California Air Resources Board (CARB) Executive Order (EO) number, which certifies they do not increase vehicle emissions. For a cold air intake to be legal in California, it must be on the vehicle manufacturer’s approved list and have an assigned CARB EO number, which you can look up on the vehicle’s product page or the CARB website.
 
Why CARB EO Numbers Are Required

• Emissions Standards: California has much stricter emissions standards than the rest of the U.S. 
• Anti-Tampering Laws: The EO number exempts the part from emission control system anti-tampering laws, as it has been verified not to increase emissions. 

How to Check if a Cold Air Intake is Legal

1. Check for an EO Number: The part itself should have a label with a CARB EO number. 
2. Verify the EO Number: You can verify the EO number on the product page of the intake manufacturer’s website, or by contacting the California Air Resources Board (CARB) directly. 
3. Check Vehicle Application: The EO number is only valid for specific vehicle model years, so ensure your vehicle’s year and engine are covered by the EO. 

Key Exceptions and Considerations

• Older Vehicles: Opens in new tabFor vehicles from 1995 or older that are non-thermostatically air cleaned, these systems do not need to comply with California regulations or have an EO number. 
• Diesel Vehicles: Opens in new tabAftermarket air intake systems on diesel vehicles do not require EO numbers. 
• Smog Check: Opens in new tabInstalling a cold air intake that does not have an EO number can cause your vehicle to fail the visual inspection at a smog check, as it will be considered an illegal modification. 

In what states are cold air intakes legal?

All K&N 57 series intakes for North American vehicles have received CARB EO numbers and are street legal in all 50 states. Some intake systems we sell beginning with the prefixes 63-, 69-, 77, & RK- are not legal for use in California and other states adopting CARB emission standards.

Do you have to tell insurance about a cold air intake?

Yes, it’s important to let your insurance company know about any modifications, no matter how small they seem. Even minor changes can impact your coverage and premiums. If you don’t disclose them, you risk having claims denied or your policy cancelled.