What Is an OEM Part?
OEM stands for Original Equipment Manufacturer. These are parts made by the same manufacturer that supplied components to the carmaker during production. In some cases, OEM parts are identical to the ones already in your car. In others, they may be produced by the same manufacturer but sold under the carmaker's branding.
OEM parts are typically sold through franchised dealerships, though you can also find genuine OEM parts through specialist suppliers.
What Is an Aftermarket Part?
Aftermarket parts are produced by third-party manufacturers rather than the original supplier. The quality of aftermarket parts varies enormously. Some are made to standards equal to or even better than the original. Others are cheap imitations that may fail early or cause further damage.
Aftermarket parts are widely available online, through motor factors, and at general car parts retailers.
Price Difference
The most obvious difference is cost. OEM parts can be significantly more expensive, sometimes by two to three times the price of a comparable aftermarket alternative. For a high-value or low-risk part like a cabin air filter, the price difference is worth factoring in. For a critical safety component like brake pads, cost should not be the only consideration.
When to Choose OEM Parts
OEM is the safer choice in these situations:
- Safety-critical components: Brakes, airbag sensors, ABS modules, steering components
- Complex electronics: ECUs, sensors, and control modules where compatibility is essential
- Cars under warranty: Using non-approved parts can void a manufacturer warranty
- Newer or specialist vehicles: Parts for newer models may only be available as OEM, and aftermarket alternatives may not yet have been properly tested
- Lease returns: If the car needs to be returned in good condition, OEM is the safer choice
When Aftermarket Parts Make Sense
Aftermarket is a perfectly reasonable choice for many parts:
- Wear items with a short lifespan: Wiper blades, air filters, spark plugs
- Older vehicles: For a car over ten years old, the cost saving from aftermarket often makes more sense
- Non-safety parts: Light bulbs, mirrors, body trim
- Performance upgrades: Some aftermarket parts actually outperform OEM versions
- Budget constraints: A quality aftermarket part from a reputable brand is better than delaying a repair
How to Judge Aftermarket Quality
Not all aftermarket parts are equal. These markers can help you spot quality:
- Brand reputation: Established manufacturers like Bosch, Brembo, NGK, Valeo, and Febi Bilstein produce parts to high standards
- OE-equivalent designation: Some aftermarket parts are marked as OE-equivalent or OE-matched, meaning they meet the same specifications as the original
- Certifications: Look for ISO or ECE certifications, particularly for parts like headlight bulbs and brake components
- Warranty: Reputable aftermarket suppliers offer warranties on their parts
Does Using Aftermarket Parts Affect Your MOT?
No. Using aftermarket parts does not affect your ability to pass an MOT, as long as the parts meet the required standards. The MOT tests the condition and performance of the vehicle, not the origin of the parts. However, safety-critical parts like brake components must still meet minimum performance standards.
What About Grey Market and Counterfeit Parts?
A small but real risk when buying online is counterfeit or grey market parts. These are parts sold as OEM or branded aftermarket, but which are actually poorly made counterfeits. Stick to reputable sellers, check for proper packaging and part numbers, and be cautious of unusually low prices on components from unknown sellers on auction sites.
Summary: Which Should You Buy?
There is no single right answer. For most repairs on an everyday car:
- Use OEM for anything safety-critical or warranty-sensitive
- Use quality branded aftermarket for routine maintenance and wear parts
- Avoid unknown-brand parts for anything that matters
Do your research, buy from trusted suppliers, and make sure the part fits your specific vehicle's make, model, year, and engine variant.
