This common misconception has been repeated often enough to be widely believed - even though it is completely false. Dealers don't like warranty work, because it pays less than normal repair work. By promoting the myth that aftermarket equipment automatically voids warranties, some dealers avoid such low-paying work. Instead, they attempt to charge customers the prime service rate for work which is rightfully under warranty. Under the Magnuson-Moss Act, aftermarket equipment which improves performance does not void a vehicle manufacturer's original warranty, unless the warranty clearly states that aftermarket equipment voids the warranty.
Most states have warranty statutes, as well, which provide further protections for vehicle owners.
In other words, that means the dealer can't wiggle out of his legal warranty obligation merely because you install aftermarket equipment. To find out if any aftermarket equipment automatically voids your vehicle's warranty, check the owners manual. Although the language seems negative, remember your vehicle manufacturer is simply saying he does not cover the aftermarket products themselves. He is not saying that the products would void the vehicle warranty. As of the 1997 model year, no properly installed equipment manufactured by Gale Banks Engineering has ever voided any vehicle manufacturer's warranty.