Genuine, OEM, OES and Aftermarket Parts: What's the Difference?

The four categories

The trade uses these words loosely, and suppliers sometimes use them to flatter a part. Here is what each one means when used precisely.

Genuine parts

A genuine part is supplied through the vehicle manufacturer's own parts system — whichever market it is supplied in — and carries the manufacturer's part number and packaging. It is the part the vehicle was built with, or the manufacturer's current replacement for it. The manufacturer may not have made the part itself; most components are made by suppliers. What makes it genuine is that it comes through the manufacturer's network, to the manufacturer's specification, with the manufacturer's identity on it.

OEM parts

OEM stands for original equipment manufacturer. In the parts trade an OEM part is one made by the company that supplies the component to the vehicle manufacturer, but sold under the supplier's own brand and in the supplier's own packaging rather than through the vehicle manufacturer's network. In some cases it is the same part off the same line without the manufacturer's logo; in others the supplier's own-brand version differs in specification, finish or included hardware. You cannot assume which from the box.

OES parts

OES stands for original equipment supplier and is often used interchangeably with OEM. Where a distinction is drawn, OES describes a part from the supplier that currently supplies the manufacturer's service network, as opposed to a supplier that once supplied the production line. In practice, treat OEM and OES the same way: made by a manufacturer's supplier, sold under the supplier's brand, and to be checked against the genuine specification rather than assumed identical.

Aftermarket parts

An aftermarket part is made by a third party to fit the vehicle, to that third party's own specification. Quality ranges from parts that meet or exceed the original specification to parts that merely fit. Aftermarket parts are sold on price, availability and, for performance parts, on being different from the original. They are not genuine and not OEM, whatever the listing says.

Comparison table

How to tell genuine from OEM from aftermarket

• The box. Genuine parts come in the manufacturer's packaging with the manufacturer's part number and, usually, a hologram or security label. OEM parts come in the supplier's box. Aftermarket parts come in the maker's box.
• The part itself. Genuine parts usually carry the manufacturer's logo and number; OEM versions of the same part often have the logo ground off or omitted. Aftermarket parts carry their own mark or none.
• The number. A genuine part number follows the manufacturer's format. An OEM number follows the supplier's format and may be cross-referenced to the genuine number on the listing.
• The seller. A part supplied through a manufacturer's dealer or distributor is genuine. A part from a motor factor under a supplier's brand is OEM or aftermarket depending on the brand.
• The price. Genuine is usually the most expensive; OEM sits below it; aftermarket varies widely. A 'genuine' part priced well below the dealer is worth questioning.

Whatever the part, ask the supplier to state the category in writing on the quote. A part described as exactly what it is causes no problems later; a part assumed to be genuine and found not to be causes several.

Which parts should be genuine?

There is no universal rule, and the decision belongs to the repairer and the customer, but the trade generally treats these as genuine-first:

• Structural and safety-critical components — body structure, airbag and restraint components, steering and braking parts on newer vehicles.
• Anything covered by a manufacturer warranty where a non-genuine part could affect a claim.
• Insurer-approved accident repairs where the repair authorisation specifies genuine parts.
• Body panels, lamps and glazing where fit, finish and ADAS compatibility depend on the exact specification.
• Prestige, performance and supercar parts where the vehicle's value depends on originality.
• Electronic modules and sensors that must match the vehicle's software.

For the parts a bodyshop needs on an insurer-approved repair, see genuine body panels sourcing. For mechanical components, genuine mechanical parts sourcing.

Genuine parts and the right to choose

In the UK, the supply of parts and repair information in the motor sector is subject to competition rules — the Motor Vehicle Block Exemption — that are designed to keep independent repairers able to compete with franchised networks. The Competition and Markets Authority's case page for the Motor Vehicle Block Exemption Regulation is the authoritative reference. The practical consequence for a workshop is that a genuine part is a choice, not an obligation, for most repairs — and equally that using a non-genuine part of appropriate quality does not by itself invalidate a vehicle's warranty. The right part depends on the job, and the important thing is that everyone involved knows which category it is.

Are OEM parts as good as genuine?

Sometimes they are the same part; sometimes they are not. The only honest answer is 'check'. Where a supplier's own-brand part is the same component that goes in the manufacturer's box, the difference is packaging, warranty route and price. Where the supplier's version differs — a different friction material on a brake pad, a different rubber compound on a bush, a different included fitting kit — the difference can matter. A reputable supplier will tell you which case applies. So will a sourcing specialist: every part REMCAM quotes is described by its actual category. See genuine OEM parts sourcing.

When genuine is no longer available

Genuine parts go NLA in the UK for models that are ten or more years old, for low-volume variants and for components a single supplier has stopped making. The options, in the order a specialist works through them:

1. Check the supersession. The number may have been replaced by a newer genuine number.
2. Check other markets. A genuine part NLA in the UK is often still supplied in mainland Europe or further afield.
3. Manufacturer heritage programmes. For older vehicles, some manufacturers reintroduce genuine parts in batches.
4. Genuine new-old stock. Unused genuine parts in period packaging held by specialist suppliers.
5. Used genuine parts. Frequently the right answer for trim, brightwork and body sections on classics.
6. OEM, OES or aftermarket. Described as exactly that, with the decision left to the repairer and the customer.
7. Remanufacture. A last resort for items nobody holds.

See obsolete and discontinued parts sourcing for how this works in practice, and classic car parts for heritage and new-old-stock routes.

What 'genuine parts only' means at REMCAM

REMCAM Automotive Ltd sources genuine manufacturer parts for the UK trade — supplied through manufacturer parts networks in whichever market they are available, with the manufacturer's part number and packaging. When a request can only be met by a different category of part, we say which category it is before you order. We are an independent parts-sourcing specialist and are not affiliated with, approved by or an authorised agent of any vehicle manufacturer. To find out what is available for a specific vehicle, send the registration or VIN via Request a Part; our guide on finding car parts by VIN or registration explains what to send.

Sources

• GOV.UK / CMA — Motor Vehicle Block Exemption Regulation
• GOV.UK — Vehicle recalls and faults