OEM vs genuine parts: what genuine, OEM, OES and aftermarket mean

Genuine parts: the carmaker’s box and the carmaker’s number

Genuine means the part passed through the vehicle manufacturer’s own parts supply. It carries the carmaker’s logo, the carmaker’s part number and, in most cases, the carmaker’s warranty on the part. A dealer parts desk sells genuine by default.

The carmaker rarely makes the part itself. A genuine alternator or brake caliper usually comes from a specialist supplier, and the carmaker buys it, boxes it and numbers it. The genuine label tells you who stands behind the part, which is useful to know before a warranty claim.

OEM, OE and OES: the supplier’s version

OEM stands for original equipment manufacturer. In the parts trade it names the company that made the part fitted to the car at the factory, and by extension the same part sold under that company’s own brand. OE (original equipment) and OES (original equipment supplier) get used for the same idea, and sellers do not use the three terms consistently.

EU competition guidelines give the closest thing to a formal definition. Original parts are made to the specifications and production standards the carmaker provides for building the vehicle, and that includes parts made on the same production line. A supplier can certify that its parts meet that standard, and the parts are then presumed original.

The catch is that the supplier’s own numbering differs from the carmaker’s. Our guide to OE supplier brands shows how to match a supplier reference back to the carmaker number.

Aftermarket parts and where OEM vs aftermarket fits

Aftermarket parts are made by companies other than the one that supplied the factory. Quality varies from maker to maker, and the part is designed to fit rather than built to the carmaker’s drawing. Our guide to OEM vs aftermarket parts covers that comparison in detail.

The same supplier brand can be original equipment on one car and aftermarket on another. A company that supplied the factory for one model may sell a matching part for a model it never supplied, under the same logo. The brand name alone does not settle which kind of part you are holding.

Telling the carmaker’s number from the supplier’s

The official parts catalog lists the carmaker’s own numbers and nothing else. Enter the VIN, open the diagram and the number beside the part is the genuine reference for that build, with any supersession applied. A number in the Volkswagen Group shape, such as 1K0 615 301 AB, is a carmaker number. A Bosch or Valeo reference printed on the same part is the supplier’s.

Many parts carry both numbers on the housing. If a number you read off a part does not appear in the catalog, try the free OEM number lookup. A number that matches no carmaker format is usually a supplier reference.

Choosing between genuine, OEM and aftermarket

Genuine costs the most and carries the carmaker’s part warranty. OEM or OES usually costs less for a part of the same specification, and it makes sense for wear items such as filters, pads and sensors once you have matched the reference. Aftermarket saves the most and needs the most checking.

In the United States, the FTC states that using aftermarket or recycled parts does not void the vehicle warranty, and a manufacturer that denies a claim must show the part caused the damage. Counterfeits are a separate risk in every group, which our post on spotting counterfeit parts covers.