The VIN check digit: what it catches and what it misses

How the ninth character of a VIN catches typos and many fake VINs, why a valid check digit is not a clean history, and what to check next before you buy.

Every used-car listing should show a VIN, the vehicle identification number. Under 49 CFR Part 565, a VIN for vehicles sold in the US has 17 characters, and one of those characters exists only to check the others. It is called the check digit, and knowing what it can and cannot tell you saves time before you spend money on a history report.

Where the check digit sits

In a 17-character VIN, characters 1 to 3 are the World Manufacturer Identifier, characters 4 to 8 describe the vehicle, character 9 is the check digit, character 10 is the model year, character 11 is the plant, and characters 12 to 17 are the serial number.

The check digit is calculated from all the other characters. If someone mistypes a single character, the calculation usually stops matching. The letters I, O and Q are never used in a VIN, so they cannot be confused with the digits 1 and 0. If you see one of them, the VIN has been copied wrong.

What a valid check digit tells you

The VIN was probably copied correctly from the car or the paperwork.
The VIN is at least shaped like a real one. The check digit catches typos and many fake VINs, and North American cars must pass it.
You can read basic facts straight from the characters: the maker, where it was built, the model year and the serial.

What it cannot tell you

A valid check digit says nothing about the car's past. Title brands, accidents and listings need the report, because they live in records, not in the 17 characters.

It also cannot prove the VIN belongs to the car in the photos. A failed check digit on a North American car is a red flag, and so is a VIN that does not match the model in the listing. Compare what the VIN decodes to with what the seller says the car is.

Free checks to run next

NHTSA offers a free public recall lookup by VIN at nhtsa.gov/recalls.
The National Insurance Crime Bureau offers a free VINCheck service that reports theft and total-loss records it holds.
Ask the seller for the title and check that its VIN matches the one on the car and in the listing.

Decode it yourself

You can paste any VIN into the free VinMojo decoder. The decoder runs in your browser, and your VIN is only sent if you ask for a report. If you want the rest of the story, a person works through the federal recall, theft and total-loss databases and title records for that VIN, starting with a Quick report at $4.99 per VIN. You pay only after we confirm the records exist.

Reports cover what public records show; they do not replace an inspection by a mechanic. Get a mechanic to look at any car before you pay for it. If you are comparing a few cars, Just A Test Drive is a sister MADITECH site with a free test drive scorecard: rate and compare up to 3 cars.