Under the Magnusson-Moss Act, aftermarket equipment that improves performance does not void a vehicle manufacturer's original warranty, unless that warranty clearly states the addition of aftermarket equipment automatically voids the warranty or that the aftermarket device is the direct cause of the failure.

In North America, vehicle and engine manufacturers cannot void a warranty if the customer adds any after-market product. A specific example is the Magnusson-Moss Consumer Product Warranty Act of 1992 that states manufacturers may not void a warranty if after-market product(s) are used or added unless that equipment manufacturer can demonstrate that the product(s) caused harm to the engine. Further, if there is a warranty claim, and the manufacturer wishes to 'blame' the after-market product, the onus and cost is on the manufacturer to prove how the product caused the issue in question. Even if they can prove a fuel additive caused a problem, they still cannot void their warranty. They (quite rightly) just don't have to pay for specific damage caused by the product.

MAGNUSON MOSS WARRANTY ACT US Code - Title 15, Chapter 50, Sections 2301-2312 Legally, a vehicle manufacturer cannot void the warranty on a vehicle due to an aftermarket part unless they can prove that the aftermarket part caused or contributed to the failure in the vehicle (per the Magnuson Moss Warranty Act (15 U.S.C. 2302(C)). If your vehicle manufacturer fails to honor emission/warranty claims, contact EPA at (202) 260-2080 or www.epa.gov. If federal warranty protection is denied, contact the FTC at (202) 326-3128 or www.ftc.gov.