The Magnuson-Moss Warranty Act is the federal law that governs consumer product warranties. Passed by Congress in 1975, the Act requires manufacturers and sellers of consumer products to provide consumers with detailed information about warranty coverage. In addition, it affects both the rights of consumers and the obligations of warrantors under written warranties.

In brief, this act provides that a manufacturer cannot threaten to void a written warranty based on the use of non-OEM (aftermarket) parts, components, and, or supplies (such as fuel or oil additives) unless it is specifically prohibited in the warranty and the manufacturer must be able to show a valid reason for such a prohibition.

In layman's terms, this means the manufacturer must be able to prove that the non-OEM part, component, or supply (additive) caused the failure. If this cannot be shown, the warranty must be honored as written.