When your vehicle needs a new part - whether it’s a brake rotor, an oil filter, or an alternator - the replacement part falls into one of three categories: OEM, OES, or aftermarket. The differences affect fit, durability, warranty compliance, and resale value. Understanding what each term means helps you make informed decisions about your vehicle’s service.
Bottom Line:
- OEM (Original Equipment Manufacturer) - made by or for the vehicle’s brand, sold in brand packaging. Required for most warranty work
- OES (Original Equipment Supplier) - the exact same part from the same factory, sold under the supplier’s own brand at a lower price
- Aftermarket - made by third-party manufacturers. Quality varies widely, from excellent to problematic
- For warranty-period vehicles, OEM is the safe choice. For routine maintenance on older vehicles, OES and quality aftermarket parts have their place
OEM Parts: What the Brand Sells
OEM stands for Original Equipment Manufacturer. These are parts made by - or made exclusively for - your vehicle’s manufacturer, sold under the manufacturer’s brand name and part number. When you buy a Volvo oil filter from Volvo Cars of Huntington, the box says Volvo, the part number matches Volvo’s catalog, and the filter meets Volvo’s exact specifications.
OEM parts are packaged and branded by the manufacturer, carry the manufacturer’s part number, and are typically the most expensive option. They’re required for most warranty and recall work, and available through franchised dealerships and authorized retailers.
The premium is worth it for warranty work, safety-critical components, and vehicles you plan to resell at high value.
OES Parts: The Same Part, Different Box
OES stands for Original Equipment Supplier. Here’s the key insight - the vehicle manufacturer doesn’t make most of their own parts. They contract with specialized suppliers.
A Volvo brake rotor might be manufactured by Brembo. Volvo buys that rotor, puts it in a Volvo-branded box with a Volvo part number, and sells it as an OEM part. Brembo also sells the identical rotor - same casting, same materials, same factory - in a Brembo-branded box with a Brembo part number. That second rotor is an OES part.
Why OES parts cost less:
- No manufacturer markup on packaging and branding
- No vehicle-brand distribution surcharge
- The supplier sells directly through their own parts channels
The quality is identical because it’s literally the same part from the same production line. The only difference is whose name is on the box.
Common OES suppliers include Bosch, Denso, Brembo, Continental, Mann-Hummel, Mahle, and NGK. Many of these names are well-known to anyone who’s spent time in a parts catalog - they’re the companies that actually engineer and manufacture the components.
"With a brand like Volvo, parts quality directly affects the ownership experience. We use OEM parts for all warranty and recall work - that's non-negotiable. For routine maintenance on out-of-warranty vehicles, we'll have an honest conversation about OES options that meet the same standards at a better price point."
General Manager, Volvo Cars of Huntington
Aftermarket Parts: The Wide Spectrum
Aftermarket parts are manufactured by third-party companies that have no direct relationship with the vehicle manufacturer. They reverse-engineer parts to fit specific vehicles and sell them - typically at significant discounts.
The quality range is enormous. Some aftermarket manufacturers produce parts that meet or exceed OEM specifications. Others cut corners on materials, tolerances, and testing. The challenge for consumers is distinguishing between the two.
Where aftermarket works well: Wear items on older vehicles (brake pads, filters, wiper blades), cosmetic pieces, and performance upgrades where the goal is exceeding OEM specs.
Where aftermarket carries risk: Safety-critical systems (brakes, steering, suspension), engine and transmission internals where material quality is critical, and electrical components where mismatched specs can trigger fault codes in modern vehicles.
How Parts Choice Affects Your Warranty
The Magnuson-Moss Warranty Act prevents manufacturers from voiding your warranty simply because you used a non-OEM part. However - if a non-OEM part causes a failure, the manufacturer can deny that specific warranty claim. For vehicles still under warranty, OEM or OES parts are the path of least resistance.
For a complete guide to maintenance timing, see our car maintenance schedule.
Impact on Resale Value
Documented service history using OEM or OES parts supports stronger resale values - particularly for premium brands like Volvo, BMW, and Audi. For mainstream vehicles, the impact is less pronounced but still real - buyers reviewing service records have more confidence in OEM-maintained vehicles.
When Each Type Makes Sense
| Scenario | Recommended Part Type | Why |
|---|---|---|
| Under warranty | OEM or OES | Warranty compliance, zero risk |
| Recall or safety campaign | OEM (provided free) | Manufacturer-supplied, required |
| Routine maintenance (post-warranty) | OES or quality aftermarket | Same quality, lower cost |
| Safety-critical repair | OEM or OES | Fitment and material precision matter |
| Older vehicle (10+ years) | Quality aftermarket or OES | Balances cost and reliability |
| Performance upgrade | Aftermarket (reputable brand) | Purpose-built to exceed OEM specs |
| Cosmetic replacement | Aftermarket | Significant savings, low risk |
What Your Dealership Uses
Franchised dealerships - including all VIP Automotive Group locations - use OEM parts for warranty repairs, recalls, and most service work. For out-of-warranty routine maintenance, some dealerships offer OES alternatives and will discuss the options with you.
Ask your service advisor. If cost is a factor, a transparent service department will tell you when an OES option exists that meets the same specification at a lower price. If you’re not sure what parts were used on your vehicle during its last service, a multi-point inspection can assess the current condition of wear items regardless of their origin.
Frequently Asked Questions
Are OES parts lower quality than OEM?
No. OES parts are manufactured on the same production line, using the same materials and specifications, as the OEM version. The only difference is branding and packaging. An OES Bosch alternator is the same alternator that would be in a Volvo-branded box - it just costs less because it doesn’t carry the vehicle manufacturer’s markup.
Will using aftermarket parts void my entire warranty?
No. Under the Magnuson-Moss Warranty Act, a manufacturer cannot void your entire warranty for using aftermarket parts. They can only deny a claim if the aftermarket part directly caused the failure in question. However, proving causation can become complicated, which is why OEM or OES parts are recommended during the warranty period.
How do I know which supplier makes my vehicle’s OEM parts?
Many OEM parts carry subtle supplier markings - a small Bosch logo stamped into a brake caliper, or a Denso marking on a sensor. Parts counter staff at your dealership can sometimes identify the original supplier, and online forums for your specific vehicle often have detailed supplier lists.
Do dealerships make more profit on OEM parts?
Generally, yes - but OEM parts include quality assurance, correct fitment guarantee, and return support that aftermarket channels may not offer. If cost is a concern, ask about OES alternatives rather than defaulting to aftermarket.
Is it worth buying OEM parts online and bringing them to a shop?
Most dealerships will not install customer-supplied parts for liability reasons, and many independent shops won’t warranty the labor if a customer-supplied part fails. Ask about OES alternatives first - the convenience and labor warranty usually make it the better approach.
