Ask three people in this trade what “OEM” means and you will get three answers, two of which contradict each other. That is not a small problem, because the word is doing the work of a guarantee in most conversations about a quote. It is worth ten minutes to get the vocabulary straight.
What do the three words actually mean?
They describe where a part came from, not how good it is. Here they are separated, in the way this workshop uses them and in the way a quote should say them.
- Genuine
- The part sold to you in the car manufacturer’s own box, with the car manufacturer’s own part number on it, through its distribution network. It is a statement about the supply chain and the packaging. It is not a statement that the carmaker made it, and usually the carmaker did not.
- OEM / OES
- The same part from the company that actually manufactured it, in that company’s own box, with its own number. Same production line, different label, different distribution chain. This is where the words start fighting, because some people use "OEM" for the carmaker’s box and some for the supplier’s.
- Aftermarket
- A part designed and made by somebody who does not supply that carmaker with that part. It can be worse than the original, identical to it, or deliberately better than it — a performance brake pad and a bargain-bin brake pad are both aftermarket, and the word tells you nothing about which one is in the box.
- Counterfeit
- Not a fourth grade. A crime. A counterfeit part is aftermarket manufacture inside somebody else’s trademark, and it is sold as genuine at genuine prices, which is what makes it dangerous rather than merely cheap.
Is there a proper definition anywhere?
Yes — in European type-approval law, and it is worth reading closely even though it does not govern anything in this country. Directive 2007/46/EC, at definition (26), says: “‘original parts or equipment’ means parts or equipment which are manufactured according to the specifications and production standards provided by the vehicle manufacturer for the production of parts or equipment for the assembly of the vehicle in question. This includes parts or equipment which are manufactured on the same production line as these parts or equipment. It is presumed unless the contrary is proven, that parts constitute original parts if the part manufacturer certifies that the parts match the quality of the components used for the assembly of the vehicle in question and have been manufactured according to the specifications and production standards of the vehicle manufacturer”.
Two things fall out of that paragraph. The first is that “original” is defined by specification and production line, never by packaging — the law does not mention a box at all. The second is that last sentence: the presumption of originality can be created by the part manufacturer certifying it, which is precisely the mechanism by which a supplier’s own-brand part is the same part.
The law defines an original part by the production line it came off, not by the box it came in. Almost every argument about parts is an argument about the box.
Does the industry even agree on the words?
No, and that is worth knowing before somebody uses one of them at you. Bosch, which is one of the largest suppliers of original equipment in the world, publishes its own glossary, and it defines the terms the opposite way round from most customers: “Original Equipment Manufacturer spare (OEM Spare) parts are produced by the entity that manufactures original parts for automakers,” while “Original Equipment Supplier or OES spare parts, also known as Automotive Aftermarket parts, are identical to Original Equipment Manufacturer (OEM) spare parts in terms of reliability and performance.”
So in a supplier’s vocabulary, “aftermarket” can mean the identical part in a different box. In a customer’s vocabulary it usually means the cheap copy. Both are in use, in the same city, on the same day. The only defence is to stop using the words as grades and start asking the question underneath them: who manufactured this, and what is the part number?
Why is the same part cheaper in the supplier’s box?
Because you are buying a shorter distribution chain, not a lesser part. Follow the two routes a single component takes. On one, it leaves the supplier’s line, is packed in the carmaker’s box, travels through the carmaker’s regional warehousing and its franchised network, and arrives with that network’s costs and its warranty inside the price. On the other, it leaves the same line, is packed in the supplier’s own box under the supplier’s own part number, and reaches a parts distributor. Same object, two ledgers.
That is not an argument that the genuine route is a waste of money. The carmaker’s box comes with the carmaker’s warranty on the part, a part number guaranteed to match your VIN, and an accountable chain from factory to counter — all of which are worth something, and on a car in warranty are worth a great deal. It is an argument for knowing which of the two you are being sold, and for being suspicious of the third possibility: a supplier-priced part in a carmaker-priced invoice.
Will a non-genuine part void my warranty?
In the United States, no — and the reasoning is worth having even where the law is different. The Magnuson-Moss Warranty Act contains a tie-in prohibition that the FTC quotes in its own business guidance: “No warrantor of a consumer product may condition his written or implied warranty of such product on the consumer’s using, in connection with such product, any article or service (other than article or service provided without charge under the terms of the warranty) which is identified by brand, trade, or corporate name.” The FTC then states the practical consequence: companies cannot “void a consumer’s warranty or deny warranty coverage solely because the consumer uses a part made by someone else or gets someone not authorized by the company to perform service on the product.”
And the honest other half, which the FTC states in the same guidance: a warrantor may still “disclaim warranty coverage for defects or damage caused by the use of unauthorized parts or service.” The principle is causation, not presence. A cheap filter does not void the warranty on your gearbox; a cheap filter that seized an engine is a different conversation, and a fair one. Two caveats we will say out loud: this is US law, it is not the law here, and we could not find a readable UAE statute or regulator page on tie-in provisions. Your warranty in this country is a contract — read what it actually says, and keep the invoices.
How do I know an aftermarket part is any good?
Start with the fact that some categories are regulated here. The Ministry of Industry and Advanced Technology operates a conformity scheme under which a supplier applies for “a UAE Certificate of Conformity for products subject to technical regulations”, confirming the products “comply with the approved standard specifications”. Which products are subject is set by “regulatory decisions issued by the Ministry of Industry and Advanced Technology”. That is a floor under the market for the categories it covers — a real one, and not a quality ranking.
Then take the counterfeit problem seriously, because it is the one that turns this from a value question into a safety question. The National, reporting in September 2018 on raids in the UAE, quoted Julian Redman, managing director of operations at an independent Dubai workshop, on how good the fakes have become: “The counterfeit boxes are very good. The holograms and printed part numbers look real but as soon as you take (the item) out of the box a trained professional should notice immediately the weight and feel is wrong.” The same report named filters and brake pads as the items most commonly found.
Notice what that quotation actually concedes: the packaging is no longer the test. The part in the hand is. Which is an argument for buying parts through somebody who handles hundreds of them, and against buying the cheapest listing online and bringing it in a carrier bag.
So when is each one the right choice?
| Situation | What usually makes sense | Why |
|---|---|---|
| Car in factory warranty | Genuine, or a supplier part with paperwork. | It removes the causation argument before it can start, and the invoice is the evidence. |
| A routine wear item — filters, pads, discs, wipers | A named supplier’s own-brand part. | Often literally the same production line, and the only difference is the distribution chain. |
| An electronic or sensor part the car must calibrate to | Genuine or the original supplier. | The part has to behave exactly as the control unit expects, not merely fit. |
| Body panels and lights on an older car | Aftermarket, chosen and checked. | Fit and finish vary; the right answer is to see the panel offered up, not to trust a category. |
| A car being kept, not sold | Whatever lasts, with the reasoning written on the quote. | The cheapest part fitted twice is the most expensive part. |
Where we would not economise
- Anything in the braking system. A pad or a hose is the one component whose failure has no second chance, and the counterfeit trade concentrates there for exactly the reason that it sells in volume.
- Airbag and restraint components. There is no way to test one before it is needed.
- Sensors the engine control unit trusts absolutely — air flow, oxygen, crank and cam position. A part that fits and reads slightly wrong is worse than a part that does not work, because the car will believe it.
- Timing components. The labour is the cost; the part is a rounding error against the labour, and against what a failure does.
- Anything that carries load into the structure. A suspension arm is a structural part with a bush in it.