The check digit lets anyone detect a mistyped or fabricated VIN. It is defined in the US federal standard 49 CFR 565 and used by ISO 3779, and it is mandatory on North-American vehicles. Tesla follows it for cars sold in North America; vehicles built in Shanghai or Berlin for other markets sometimes do not match, so a mismatch there is not proof of a fake.
The algorithm
- Transliterate each letter to a number: A=1, B=2, C=3, D=4, E=5, F=6, G=7, H=8, J=1, K=2, L=3, M=4, N=5, P=7, R=9, S=2, T=3, U=4, V=5, W=6, X=7, Y=8, Z=9. Digits keep their value.
- Multiply each value by the weight of its position:
8 7 6 5 4 3 2 10 0 9 8 7 6 5 4 3 2. Position 9 (the check digit itself) has weight 0. - Add all the products.
- Divide by 11. The remainder is the check digit; a remainder of 10 is written as
X.
Worked example
Take the illustrative VIN 5YJ3E1EA2KF317000:
| Pos | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Char | 5 | Y | J | 3 | E | 1 | E | A | 2 | K | F | 3 | 1 | 7 | 0 | 0 | 0 |
| Value | 5 | 8 | 1 | 3 | 5 | 1 | 5 | 1 | – | 2 | 6 | 3 | 1 | 7 | 0 | 0 | 0 |
| Weight | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 10 | 0 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 |
| Product | 40 | 56 | 6 | 15 | 20 | 3 | 10 | 10 | 0 | 18 | 48 | 21 | 6 | 35 | 0 | 0 | 0 |
The products add up to 288. 288 ÷ 11 = 26 remainder 2, so the check digit must be 2 – exactly what the ninth character of that VIN is.
What if the check digit does not match?
- Most likely a typo. Re-read the VIN from the windshield or door jamb. The classic confusions are 0/O, 1/I, 5/S, 8/B and 2/Z. TeslaVin tests every single-character change and suggests the corrections that produce a valid Tesla VIN.
- A non-North-American build. The check digit is not legally required elsewhere, so some Shanghai and Berlin VINs do not satisfy the formula.
- A fake or altered VIN. If the digit fails on a car that was sold in the US or Canada, treat it as a red flag and verify the VIN physically and through official records.
Why the weights?
The weights are chosen so that the most common mistakes – a single wrong character, or two neighbouring characters swapped – change the sum and are caught. It is not a security feature: anyone who knows the formula can compute a valid check digit for an invented VIN, which is why a valid digit alone never proves a car is genuine.
