Vehicle Identification Numbers (VIN codes)/Check digit
One element that is fairly consistent in VIN numbers is the use of position 9 as a Check digit, compulsory for vehicles in North America and used fairly consistently even outside this rule.
If trying to validate a VIN with a check digit, first either: (a) remove the check digit for the purpose of calculation; or (b) utilize the multiplicative property of zero in the weight to cancel it out. You should later compare the old value of the check-bit, with the new to ensure the VIN's validity.
Contents
Overview of the process[edit]
An overview of the process for calculating a VIN's check digit is as follows:
- Remove all of the letters from the VIN by transliterating them with their numeric counterparts. Numerical counterparts can be found in the table below.
- Multiply this new number, the yield of the transliteration, with the assigned weight. Weights can be found in the table below.
- Sum the resulting products.
- Modulus the sum of the products by 11, to find the remainder.
- If the remainder is 10 replace it with X.
Transliterating the numbers[edit]
Transliteration consists of removing all of letters and substituting them with their appropriate numerical counterparts. These numerical alternatives can be found in the following chart. I, O and Q are not allowed, and can not exist in a valid VIN; for the purpose of this chart, they have been filled in with N/A (not applicable). Numerical digits use their own values.
A: 1 | B: 2 | C: 3 | D: 4 | E: 5 | F: 6 | G: 7 | H: 8 | N/A |
J: 1 | K: 2 | L: 3 | M: 4 | N: 5 | N/A | P: 7 | N/A | R: 9 |
S: 2 | T: 3 | U: 4 | V: 5 | W: 6 | X: 7 | Y: 8 | Z: 9 |
S is 2, and not 1. There is no left-alignment linearity.
Weights used in calculation[edit]
The following is the weight factor for each position in the VIN. The 9th position is that of the check digit. It has been substituted with a 0, which will cancel it out in the multiplication step.
Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Weight | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 10 | 0 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 |
Worked example[edit]
Consider the hypothetical VIN 1M8GDM9A_KP042788, where the underscore will be the check digit.
VIN | 1 | M | 8 | G | D | M | 9 | A | _ | K | P | 0 | 4 | 2 | 7 | 8 | 8 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Value | 1 | 4 | 8 | 7 | 4 | 4 | 9 | 1 | _ | 2 | 7 | 0 | 4 | 2 | 7 | 8 | 8 |
Weight | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 10 | 0 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 |
Products | 8 | 28 | 48 | 35 | 16 | 12 | 18 | 10 | 0 | 18 | 56 | 0 | 24 | 10 | 28 | 24 | 16 |
- The VIN's Value is calculated from the above table, this number will be used in the rest of the calculation.
- Copy over the weights from the above table.
- The products row is a result of the multiplication of the vertical columns: Value and Weight.
- The products (8,28,48,35..24,16) are all added together to yield a sum of 351
- One of the following operations:
- 351 % 11 = 10 (where % is a modulo operator)
- 351 ÷ 11 = 31 10/11
- 351 ÷ 11 = 31.9090-
- The check digit is 10, so it has been transliterated into X.
With a check digit of 'X' the VIN: 1M8GDM9A?KP042788 is written with the check bit as: 1M8GDM9AXKP042788.
Straight-ones (seventeen consecutive '1's) will suffice the check-digit. This is because a value of one, multiplied against 89 (sum of weights), is still 89. And 89 % 11 is 1, the check digit. This is an easy way to test a vin-check algorithm.