The car you bought, whether it is German-made, American-made, Japanese-made etc., is made up of parts made by hundreds of other companies. All car manufacturers use independent companies to design and make various components that make up a car. So what does this mean for you the consumer?
What is a Genuine Part?
A Genuine part is a part that is originally put in your vehicle when it was new and has the car manufacturer's logo on it. This does not mean the product is actually made by the car manufacturer, it is often times made by a different company but the car manufacturer's logo is added. These are the most expensive parts as you are paying for the car manufacturer's logo.
Most people believe that they MUST replace a part on their vehicle with a Genuine part, i.e. a part bearing the manufacturer's logo or it will void the warranty on the vehicle. THIS is a MYTH and it is illegal under The Magnuson-Moss Warranty Act for ANY car manufacturer to deny warranty based on the use of an aftermarket or used part. Also, a warranty cannot be voided because you use other than a dealership or even yourself to perform repair on your vehicle.
What is an OEM Part?
An OEM (Original Equipment Manufacturer) part is a part built by the same company that built the original product for the car maker. It is almost the exact same part that is in your car, except it does not have the car maker's logo. These parts can very slightly due to manufacturing changes and are cheaper as you are not paying for the privilege of having the car maker's logo. Basically, the only difference between Genuine and OEM is the box it is shipped in.