A lot number is a way of identifying the source, or "lot", of a particular product. On a vehicle, the lot number is part of the vehicle identification number, which is a unique code that is used to trace the origin and manufacturer of the vehicle.
In cases of a recall of a vehicle part, the VIN is used to identify the source of components. If the vehicle owner has concern about a specific part or location in the history of the vehicle, the VIN is key to tracing where the vehicle originated, what type of parts were used and any safety concerns with a part.
When searching for a particular lot number to find the history of the car, sites such as CarDetective.com, AutoCheck.com and Carfax.com offer search engines for owners to enter the lot number and VIN to find their specific vehicles.
All over-the-road vehicles are required by law to have a 17-digit VIN of numbers and letters. The VIN contains the country of origin of the car, the make and model, and the body style of the car. The U.S. Department of Transportation does not maintain a list of car VINs; the numbers are supplied by the manufacturer.