In fact, the Magnuson-Moss Warranty Act, which is enforced by the FTC, makes it illegal for manufacturers or dealers to claim that your warranty is void or to deny coverage under your warranty simply because someone other than the dealer did the work. That said, there may be certain situations where a repair may not be covered. For example, if you or your mechanic replaced a belt improperly and your engine is damaged as a result, your manufacturer or dealer may deny responsibility for fixing the engine under the warranty. However, according to the FTC, the manufacturer or dealer must be able to demonstrate that it was the improper belt replacement — rather than some other defect — that caused the damage to your engine. The warranty would still be in effect for other parts of your car.
