Under the provisions of the Magnuson-Moss Warranty Act of 1975, an automotive dealership/carmaker cannot void your warranty because your vehicle has been modified with aftermarket parts. They (the manufacturers) have to prove that the failure was the direct result of the installed aftermarket part. Unfortunately, too many folks have gone to a dealer to have warranty service performed on their modified vehicle only to have the dealer refuse to cover the defective items. The dealer usually states, that because of the aftermarket parts installed, the warranty is void (without even attempting to determine whether or not the aftermarket part caused the problem). This is illegal...period. Examples where the dealership will not cover your repairs under warranty You install an aftermarket air dam system to channel more air to the cold air intake system that you installed. The air dam system causes the vehicle to overheat because it restricts airflow over the radiator. As a result of overheating, the engine blows a head gasket and a cylinder head is warped. The car is still under warranty. You take it to your dealer and they determine that the aftermarket air dam system caused the overheating and thus the cylinder head damage and gasket failure. The carmaker is not obligated to perform any repairs under the provisions of the warranty.