What all seventeen characters mean
A VIN is five fields, not seventeen arbitrary characters. Once you can see the fields you can read most of a car off the plate without decoding anything.
A 2003 Honda Accord built in Marysville, Ohio.
World Manufacturer Identifier position 1 to 3
Who built it and where. The first character is the region, the second the country and manufacturer, the third the vehicle type or division. A manufacturer building under 1,000 vehicles a year gets 9 in position three, and its identity moves to positions 12 to 14.
Vehicle Descriptor Section position 4 to 8
Model, body, engine, restraint system. Manufacturers assign these five characters themselves, so there is no universal table: the same letter means different things to Honda and to Ford. This is why a decoder has to hold every manufacturer’s scheme rather than compute an answer.
Check digit position 9
A weighted checksum over the other sixteen characters, and the reason a mistyped VIN is usually detectable without looking anything up. North American VINs must satisfy it. Many imports built for other markets do not.
Model year position 10
A 30-year cycle that runs A to Y skipping I, O, Q and U, then 1 to 9, then repeats. So this character alone is ambiguous: A is 1980 and 2010 both. Position seven breaks the tie, because it is numeric for 1980 to 2009 and alphabetic from 2010.
Assembly plant position 11
The specific factory, assigned by the manufacturer. Two identical cars off two lines differ here, which is how a recall can be scoped to one plant.
Serial number position 12 to 17
The sequential build number. For a low-volume manufacturer the first three of these six carry the manufacturer identity instead, continuing the WMI.
The three letters that never appear
I, O and Q are excluded from the VIN alphabet entirely. The reason is physical rather than digital: a VIN is stamped into a metal plate and read at an angle through a windscreen, where I cannot be told from 1 and O cannot be told from 0. Rather than accept a permanent ambiguity in a number used for recalls, titles and theft recovery, the standard removed all three.
So if you are reading a VIN off a car and you think you see an O, it is a zero. Every time. This is also the cheapest possible validation: any string containing I, O or Q is not a VIN, and no lookup is needed to know that.
How the check digit works
The ninth character is a weighted modulus-11 checksum over the other sixteen. Each letter transliterates to a number, each position carries a weight, the products are summed, and the remainder on division by 11 is the check digit, written X when it comes to 10.
It is mandatory for vehicles sold in North America and optional elsewhere, which is why a genuine grey-market import frequently fails it. A failed check digit here is reported as a caution, never as a rejection.
Why the model year is ambiguous on its own
Position ten runs a 30-year cycle: A to Y skipping I, O, Q and U, then 1 to 9, then it starts again. A means 1980 and it also means 2010. The tiebreaker is position seven, which manufacturers keep numeric for model years 1980 to 2009 and alphabetic from 2010, specifically so the cycle can be resolved from the VIN alone.
Try one
Structure per ISO 3779 and 49 CFR 565. Decoding against NHTSA vPIC, 888 manufacturer prefixes indexed. Browse by make.