When a mechanic replaces a part on your car, are they putting in a factory part from the manufacturer — or something else entirely? The answer matters more than most people realize, and the rules around disclosure are something every car owner should understand.
Short answer: shops are not required to use OEM (Original Equipment Manufacturer) parts. But they are required to tell you what they're using. And you have the right to request OEM parts if you want them.
What's the Difference?
OEM parts are made by the original manufacturer — or an approved supplier — and are identical to what came on your car from the factory. They're designed specifically for your make and model, they carry the manufacturer's warranty, and they're generally more expensive.
Aftermarket parts are made by third-party companies and designed to fit your vehicle. Quality varies enormously. Some aftermarket parts are perfectly fine — in some cases they're actually better than OEM. Others are cheaply made knockoffs that wear out faster or don't fit as precisely as they should.
Rebuilt or remanufactured parts are used components that have been restored to working condition. They're common for alternators, starters, and brake calipers. Quality depends heavily on who did the rebuilding.
When Aftermarket Is Fine
Routine maintenance items are usually fine with quality aftermarket parts. Air filters, wiper blades, belts, hoses, spark plugs — a reputable aftermarket brand like Bosch, Denso, or Gates is often equivalent to OEM at a lower price. Any honest mechanic will tell you this.
Where it gets more complicated is anything that directly affects safety.
When OEM Parts Actually Matter
Brake components, airbag sensors, steering system parts, and ADAS (advanced driver assistance system) components are areas where quality control really counts. A counterfeit or substandard brake caliper isn't just an inconvenience — it's a safety issue.
The same goes for anything that has to communicate with your car's computer systems. Modern vehicles are full of sensors that need to be precisely calibrated. A poorly made component can trigger warning lights, cause erratic behavior, or simply fail to perform when it matters most.
If your car is still under warranty, using certain aftermarket parts may affect coverage in specific situations — though federal law (the Magnuson-Moss Warranty Act) generally prohibits manufacturers from voiding your entire warranty just because you used aftermarket parts.
What Shops Are Required to Disclose
In most states, repair shops are required to disclose whether they're using new, used, rebuilt, or aftermarket parts — either on the estimate or before work begins. You should see this information in writing before you authorize any repair.
If a shop quotes you a price and doesn't specify what kind of parts they're using, ask. If they're vague or evasive, that's a red flag.
This same standard applies to mobile mechanics. Just because someone works out of a van doesn't mean the disclosure rules don't apply to them. A professional mobile mechanic will be upfront about parts sourcing.
How to Protect Yourself
Before authorizing any repair, get written answers to these questions:
- Are you using OEM, aftermarket, or rebuilt parts?
- What brand are the parts?
- What warranty do the parts carry?
- Will using aftermarket parts affect my vehicle warranty?
If you want OEM parts, say so — in writing. The shop can quote you the difference in cost, and you can decide from there. Most reputable shops will accommodate the request without pushback.
The goal isn't to be paranoid about every air filter. The goal is to ask the right questions for the repairs that matter.
Not sure what questions to ask before dropping your car off? Our repair checklist and consumer guide walks you through it step by step.