How to find a car part number (OE number)
Last updated: 4 Nov 2026
The part number is the surest way to know a used part will fit. Two cars that look identical can need different parts, but the same part number means the same part. Here's where to find it, and what to do if you can't.
Where the number is
- On the part itself: a sticker, a stamped or cast number, or a label on a plastic housing. Headlights, ECUs, alternators and starter motors nearly always have one.
- On your old part's box or invoice, if it was replaced before.
- From a main dealer's parts desk: give them your VIN and they can look up the exact original part number, usually free.
OE, OEM and aftermarket numbers
- OE (original equipment): the car maker's own number, as used by the dealer. Breakers list used parts by this number.
- OEM: the number of the company that made the part for the car maker (Bosch, Valeo, Denso and so on). It can be a different number for the same part.
- Aftermarket: other brands' replacements, with their own numbers and a cross-reference to the OE one.
Your VIN and engine code
The VIN (vehicle identification number) is 17 characters, on your V5C logbook, at the bottom of the windscreen and on a plate in a door pillar. It identifies your exact car, so it's what dealers and good sellers use to confirm a part. The engine code is stamped on the engine block or on a sticker under the bonnet, and matters for anything engine-related (used engines and gearboxes).
Searching by part number or registration
On Vehicle Part Finder you can type a part number into the search, or add your registration to see only parts listed as fitting your car. If you're unsure, message the seller with your part number and reg before you buy. Search for a part, or read how to find the right used part.