2016 Altima with 110k miles, P0420, and the OE cat is $1,800.

In Florida, installing an aftermarket catalytic converters is legal if it meets certain requirements:

Federal Law (Applies Nationwide):

• The aftermarket converter must be EPA-certified and listed on the manufacturer's application guide for your vehicle.
• It must be installed per the manufacturer's instructions.
• The converter must match the original in performance and emissions control.

Florida Specifics:

• Florida follows Federal EPA guidelines for emissions-related parts.
• The state does not require emissions testing for most vehicles (except in limited areas like Miami-Dade for certain model years), so enforcement is typically minimal unless there's a visible smoke issue or noise violation.

Key Considerations:

• A $250 universal converter may not be EPA-certified or properly sized for a 2016 Altima 3.5L V6.
• Universal fit converters often require welding and may not flow correctly, risking repeat P0420 codes.
• Installing a non-compliant converter could violate 40 CFR Part 85, which prohibits tampering with emissions controls.

Recommendation: Verify the converter is EPA-certified and appropriate for your engine. If the customer insists on the cheap option, document that it may not resolve the issue or meet legal standards. For compliance and reliability, recommend a direct-fit aftermarket unit from a reputable brand (e.g., Walker, MagnaFlow) that’s EPA-certified.

Installing an uncertified or improperly rated converter is risky—both legally and mechanically.

Florida has no state emissions testing program, so there is no state inspection barrier to installing a universal converter. However, federal law (Clean Air Act §203(a)(3)(B)) still applies.

The Rules:

1. EPA Certification is Mandatory: The converter must be EPA-certified for that specific vehicle application (2016 Altima, engine family, test group). "Universal" refers to fitment (pipe diameter/length), not legal certification. A $250 generic unit is almost certainly not EPA-certified for a 2016 Nissan.
2. CARB vs. EPA: Since FL follows federal standards, you need an EPA-compliant unit (not CARB, which is required in CA/CO/NY/ME). EPA units are cheaper than CARB but still typically $400–$700+ for this vehicle.
3. Installation Requirements (40 CFR §86.1806): Must be the same type (e.g., 3-way, close-coupled location). Must be installed in the exact same location as OE. Must not cause a "Check Engine Light" (P0420) due to insufficient oxygen storage capacity. You must complete EPA Form 3520-1 (or equivalent documentation) retaining proof of certification for the vehicle owner.

The Reality: A $250 universal converter will almost certainly fail to extinguish the P0420 on a 2016 vehicle with 110k miles. The downstream O2 sensor monitors catalyst efficiency via oxygen storage; cheap universals lack the precious metal loading to pass the monitor.

Recommendation: Do not install the $250 unit. It creates federal liability for you (tampering violation) and a comeback for the shop. Quote a certified EPA aftermarket converter (Walker, Eastern, MagnaFlow EPA lines) or OE. If the customer refuses, document the refusal and federal requirements on the RO.