How to check a VIN before sending an endorsement

Published 16 October 2026. Updated 16 October 2026.

A client types a VIN into an email from the cab of a truck. One digit is wrong. The request goes to the carrier, the endorsement is issued, and the policy now lists a vehicle that does not exist. The mistake surfaces months later at a claim, when it is expensive to fix.

Most of these errors can be caught in under a minute with the arithmetic built into the VIN itself. This guide explains what a VIN is, how the check digit works, and how to run the test by hand. It belongs next to the guide to adding a vehicle to a commercial auto policy, which covers the rest of the request.

What is in a VIN

A VIN is 17 characters made of digits and capital letters. The letters I, O and Q are never used. For vehicles built for the North American market the characters are laid out as follows.

• Positions 1 to 3: the manufacturer.
• Positions 4 to 8: vehicle attributes such as model and body type.
• Position 9: the check digit, a digit from 0 to 9 or the letter X.
• Position 10: the model year.
• Position 11: the plant.
• Positions 12 to 17: the serial number.

The check digit is calculated from the other sixteen characters. If any of them changes, the calculated value usually no longer matches the ninth character, and that mismatch is the signal.

The quick checks, before any arithmetic

1. Count the characters. There must be exactly 17. A client who types 16 has dropped one.
2. Look for I, O and Q. Any of these means a mistyped character, usually a 1 or a 0.
3. Look at position 10. It encodes the model year. If the client says it is a 2024 vehicle and position 10 does not stand for 2024, one of the two is wrong.
4. Compare it with a document. The title, registration or bill of sale shows the VIN. Compare character by character, not by eye over the whole string.

The check digit test, step by step

Each character is turned into a number, multiplied by a weight for its position, and the products are added. The remainder after dividing by 11 must equal the ninth character.

1. Convert letters to numbers. Digits keep their value. Letters use this table:

1. Apply the weights, by position from 1 to 17: 8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2. Position 9 has weight 0, so the check digit does not count toward its own sum.
2. Multiply and add all seventeen products.
3. Divide the sum by 11 and take the remainder. A remainder of 10 is written X. Any other remainder is written as the digit.
4. Compare with the ninth character.

Worked example

Take the VIN 1M8GDM9AXKP042788.

The products add up to 351. Dividing by 11 gives 31 with a remainder of 10. A remainder of 10 is written X, and the ninth character is X. The VIN passes.

Now change one character, say the 4 in position 13 to a 5. The sum rises by 6 to 357, the remainder becomes 5, and the expected ninth character is 5, not X. The VIN fails.

What a pass and a fail mean

• A pass means the VIN is internally consistent. It does not prove the VIN belongs to this vehicle. Two characters swapped in a way that keeps the sum can pass, a letter typed for another of the same value (B, K, S and 2 all count as 2) passes, and a wrong but valid VIN passes. Still compare it with the title.
• A fail means something is off: a typo, a misread character, or a vehicle that does not follow the North American rule. Do not correct the VIN yourself. Do not try the "nearby" VINs that would pass. Go back to the client and ask for a photo of the dashboard plate or the title.

A short routine for every change email

• Count 17 characters and look for I, O or Q.
• Run the check digit, or paste the VIN into a decoder such as NHTSA's VIN decoder.
• Compare year, make and model with what the VIN decodes to.
• Search the declarations page or vehicle schedule for the same VIN, to avoid a duplicate.
• If anything fails, reply to the client with the VIN as they wrote it and ask them to confirm it from the title.

How EndorseDesk does this step

EndorseDesk runs the VIN checks as code, not as a model's opinion. When it reads a vehicle change from a client's email, it ignores spaces and hyphens, checks that the VIN is 17 characters with no I, O or Q, and works out its check digit. It runs the check digit test on every VIN, whatever market the vehicle was built for, so treat a failed check as a question for the client. If you upload the declarations page, it also looks for the VIN there: a vehicle to add that is already listed, or a vehicle to remove that is not, is flagged. A VIN that fails is shown as written and flagged in the items to check; it is never corrected or replaced with a guess.

It does not decode the VIN or compare it with the year, make and model, so that step stays with you.

The same field sheet gives the email line behind the VIN, so you can see what the client typed. A second, stronger AI model reviews every result and lists what is left for you to decide; the drafting model corrects the serious problems the review finds, and code checks every correction. Results are not verified by a person. EndorseDesk sends nothing to the carrier. You can sign up and try it on a real email.

Questions

If a VIN passes the check digit test, is it definitely right?

No. It catches nearly every single wrong character and nearly every swap of two neighbouring characters, but not all errors. A letter typed for another of the same value (A, J and 1 all count as 1) passes, and so does a valid VIN of a different vehicle. Compare it with the title or registration too.

Why would a real VIN fail the check digit test?

The 17-character VIN with a check digit has been required in the United States since the 1981 model year. Vehicles built before then, and some built for other markets, do not follow the rule, so a failed check is a reason to ask, not proof of a typo.

Which letters can never appear in a VIN?

The letters I, O and Q are not used, because they are easily confused with 1 and 0. If a client's VIN contains one of them, it has been mistyped or misread.