VIN Validation - Part II

Decoding information from vehicle Identication Number is simple. Each manufacturer utilizes the vehicle descriptor section in the manner they see fit. The first section is called the WMI, and is the first 3 characters of the VIN. It is issued by the Society of Automotive Engineers. There is much confusion surrounding how the WMI works and how it is assigned, I will provide an explanation.

The first 3 characters of a VIN issued by SAE, they are unique. The first 2 characters are specific to the country that the original vehicle was built-in. Such as General Motors was issued 1G for vehicles built in the United States. Additional sections which are standard across all manufacturers are the VDS, Check Digit, Year, Plant, and Production Sequence.

The SAE attempts to issue the second character of the WMI as the first letter of the manufacturer. However, in order to create divisions (Chevrolet, Cadillac etc), the 3rd character are used to create more detail for the manufacturer. Such as 1G1 is a Chevrolet, while 1G2 is a Pontiac both built in the United States. Most manufacturers use it to determine the line of the vehicle, like 1GC is a Chevrolet Truck. To complicate matters further there separate layouts for vehicle manufacturers with less than 500 vehicles.

The system was designed so that letters come before numbers and numbers are 1-0, where 0 being the like 10. Depending on how many vehicles are created by the manufacturer each year the VIN has 2 different possible layouts shown below.

Vehicles with more than 500 produced

WMI VDS Check Digit Year Plant Production Sequence
1 g 3 g r 6 2 h 5 1 4 0 5 5 5 6 2

With less than 500 vehicles, the following is used, this is indicated a 9 in the 3rd digit.

WMI VDS Check Digit Year Plant WMI Production Sequence
1 g 3 g r 6 2 h 5 1 4 0 5 5 5 6 2

Years are encoded at the 10 digit. The code values are between 0-29 added to 1980. The codes began to wrap around and were begain to be used again starting in 2010. In order to validate a VIN there is an encoded check digit. The validation routinue replaces characters to a numeric equivalent. The position of each character has a weighted value, which is multipled by the numeric replacements. The value of the sum of the multipled weights is used against a modulus of 11. The remaining value is then encoded into the VIN.

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