Why does my VIN fail the check digit?

Nine times out of ten it is a typo: a letter I read as a 1, a letter O read as a 0, or two characters transposed. Re-read the VIN off the vehicle rather than off a listing. If it still fails and the vehicle was not built in North America, the check digit may simply not be in use, because plenty of European and Asian manufacturers do not calculate one.

Does a failing check digit mean the VIN is fake?

Not on its own. It means the number as written is not internally consistent. On a US, Canadian or Mexican vehicle that is worth taking seriously, so check the number against the door jamb and the title before you go further. On an import it is often normal.

Can two vehicles have the same check digit?

Constantly. It is one character with eleven possible values, so roughly one in eleven VINs shares any given check digit. It proves nothing about uniqueness; it only catches mistakes in transcription.

Does the decoder require a valid check digit?

No. The free decoder will look up any structurally valid 17-character VIN and tells you separately whether the check digit matched. Blocking on it would refuse perfectly genuine imports.

VIN position 9

VIN check digit: is my VIN valid?

The ninth character of a VIN is not information about the vehicle. It is a checksum calculated from the other sixteen characters, and its only job is to catch a VIN that has been written down wrong.

How it is calculated, why a genuine VIN can still fail it, and what to do when yours does.

How it works

1. Turn letters into numbers. Each letter has a fixed numeric value: A, J and 1 all count as 1, B, K and S all count as 2, and so on through the table below. Digits count as themselves.
2. Multiply by position weight. Each of the seventeen positions carries a fixed weight: 8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2. Position 9 is weighted zero, which is what keeps the check digit out of its own sum.
3. Add it all up and divide by 11. The remainder is the check digit. A remainder of 10 is written as the letter X, the only place an X can legitimately appear in position 9.

The rule is set out in the federal VIN standard and is mandatory for vehicles manufactured in or imported into the United States by North-American manufacturers. It is optional everywhere else, which is the single biggest reason a real VIN fails it.

Letter values

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

I, O and Q are absent because they never appear in a VIN at all.

Worked example

The full calculation for 1FMDU34X7PUD75574, run by the same code that validates VINs on this site.

Check-digit calculation for 1FMDU34X7PUD75574
Position	Character	Value	Weight	Product
1	1	1	8	8
2	F	6	7	42
3	M	4	6	24
4	D	4	5	20
5	U	4	4	16
6	3	3	3	9
7	4	4	2	8
8	X	7	10	70
9	7	7	0	none (the check digit itself)
10	P	7	9	63
11	U	4	8	32
12	D	4	7	28
13	7	7	6	42
14	5	5	5	25
15	5	5	4	20
16	7	7	3	21
17	4	4	2	8
Total				436

436 ÷ 11 leaves a remainder of 7, so the check digit must be 7, which is exactly what sits in position 9 of this VIN. It is valid.

Why is my VIN invalid?

You typed I, O or Q

Those three letters are not used in VINs. What looks like an O is a zero and what looks like an I is a one. This is the most common cause by a distance.

A character is missing or doubled

A VIN is exactly seventeen characters, with no spaces and no dashes. Sixteen or eighteen means something was dropped or repeated while copying.

Two characters are transposed

The weights are chosen so that swapping two adjacent characters almost always changes the checksum. That is the failure the check digit was designed to catch.

The manufacturer does not use one

Many vehicles built in Europe and Asia carry a position 9 that was never calculated. A German or Japanese VIN failing the test is usually telling you nothing at all.

Our decoder does not refuse a VIN over the check digit. It reports whether the number passed, then decodes it regardless. You can see the result for any VIN on the free decoder. If the check digit fails on a US-built vehicle and the number matches the plate, that is the point to be suspicious rather than the point to stop reading.

Questions about the check digit

Why does my VIN fail the check digit?: Nine times out of ten it is a typo: a letter I read as a 1, a letter O read as a 0, or two characters transposed. Re-read the VIN off the vehicle rather than off a listing. If it still fails and the vehicle was not built in North America, the check digit may simply not be in use, because plenty of European and Asian manufacturers do not calculate one.
Does a failing check digit mean the VIN is fake?: Not on its own. It means the number as written is not internally consistent. On a US, Canadian or Mexican vehicle that is worth taking seriously, so check the number against the door jamb and the title before you go further. On an import it is often normal.
Can two vehicles have the same check digit?: Constantly. It is one character with eleven possible values, so roughly one in eleven VINs shares any given check digit. It proves nothing about uniqueness; it only catches mistakes in transcription.
Does the decoder require a valid check digit?: No. The free decoder will look up any structurally valid 17-character VIN and tells you separately whether the check digit matched. Blocking on it would refuse perfectly genuine imports.

Try it on your own vehicle

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