The Magnusson-Moss Warranty - Federal Trade Commission Improvement Act of 1975 protects consumers from such fraudulent activity by new car dealers. Under this Act, aftermarket equipment that improves performance does not void a vehicle manufacturer's original warranty, unless the warranty clearly states the addition of aftermarket equipment automatically voids your vehicle's warranty or if it can be proven that the aftermarket device is the direct cause of the failure.
The easiest way to check this is to look in your owner's manual under, "what is not covered". Under Magnusson-Moss Act a dealer must prove, not just vocalize, that aftermarket equipment caused the need for repairs before they can deny warranty coverage. If they cannot prove such claim-or offer an explanation- it is your legal right to demand compliance with the warranty.
The Federal Trade Commission (202.326.312
administers the Magnusson-Moss Act and monitors compliance with warranty law.
make sure they can PROVE the extra 3 hp to the wheels actually caused the failure!