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What Is A VIN Number?

History of VIN numbers in the US

First VIN System: 1949 to July 1964
The VIN for cars produced through July 1964 is merely a production serial number. It is necessary to know what model the vehicle is. No other information can be derived from the serial number.

Second VIN System: August 1964 to July 1980
Beginning in August 1964, a new system was initiated that included vehicle model and year, along with the serial number. The first two digits indicate the model, the third digit indicates the year, and the fourth through tenth digits indicate the serial number.

Due to the difficulty of differentiating 60's vehicles from 70's or 80 vehicles, the following rules apply:

1965-1969 vehicles have a 9-digit VIN unless production exceeded 1 million, in which case the VIN is 10 digits, with the fourth digit being 1. 
1970-1979 vehicles have a 10-digit VIN, with the fourth digit of 2 or 3. 
1980 vehicles have a 10-digit VIN, with the third digit of A.

Third VIN System: 1981 to current models
Due to federal regulations, 1981 and newer vehicles are required to use a 17-digit VIN system. With this system, it is now possible to determine not only the year, model and serial number, but also the country of manufacture, body style, engine type, restraint system, and manufacturing plant.

The Vehicle Identification Number was originally described in ISO Standard 3779 in February 1977 and last revised in 1983. The ISO-VIN was designed to identify motor vehicles, trailers, motorcycles and mopeds and consists of three sections: 

VDS - Vehicle Descriptor Section. These 6 characters occupy positions 4 through 9 of the VIN and may be used by the manufacturer to identify attributes of the vehicle. 

VIS - Vehicle Identifier Section. The last 8 characters of the VIN are used for the identification a of specific vehicle. The last four characters shall always be numeric. 

ISO 3779 makes a provision for a code for the year in which a vehicle is built. When a manufacturer uses a year code, ISO recommends that the 10th position of the VIN is used. 

The same applies to the use of a factory code. When a manufacturer uses a factory or plant code, ISO recommends that the 11th position of the VIN is used. In the VIN-code, capital letters A through Z and numbers 1 through 0 may be used, except the letters I, O and Q for obvious reasons. No signs or spaces are allowed in the VIN.

The European Union has issued a directive to the effect that a VIN must be used for all road vehicles in the EU member states. This directive complies with the ISO Standard but a year digit or factory code is not mandatory. Also, it is left to the choice of the manufacturer whether the VDS is actually used for vehicle attributes or not. The system only applies to motor powered vehicles with at least four wheels capable of speed above 25 km/h and trailers.

VINs in the United States

In North America, a system is used that is far more stringent than the ISO Standards but is "backward compatible." Here, the VIN is divided into four sections: 

The second section consists of five characters (VIN positions 4-8) and identify the attributes of the vehicle. For each type of vehicle (passenger cars, MPV's, trucks, buses, trailers, motorcycles, incomplete vehicles other than trailers), different information is required. For cars, MPV's and light trucks it is required that the first two characters of this section are alphabetic, the third and fourth shall be numeric and the fifth alphanumeric. This section is the VDS in ISO 3779 but there it comprises another position of the VIN; 

The third section consist of one character which is the check digit, calculated over the other 16 characters of the VIN. This character can be numeric or the letter X; 

The fourth section consists of eight characters on positions 10-17 of the VIN. The last five shall be numeric for cars, MPV's and light trucks and the last four shall be numeric for all other vehicles. The first character represents the vehicle model year, the second character represents the plant of manufacture. The third through eighth characters are a sequential production number (for manufacturers producing more than 500 vehicles per year). For other manufacturers, the sixth, seventh and eight position represent the sequential production number.

This section confirms to the VIS in ISO 3779. 

Note that (in the US regulations) no mention is made of WMI, VDS or VIS. Also, there is no mention of the third digit being a "9" in case of the smaller manufacturers. However, the examples I found of US WMI's of smaller manufacturers all have the 9 as third digit. 

NSX VIN Interpretation

What is a Check Digit and how is it calculated?

Regulations both in the United States of America and Canada require that on the 9th position of the Vehicle Identification Number a check digit is used. In North America, the check digit is considered to be the third section of the VIN. Its purpose is to provide a means for verifying the accuracy of the VIN transcription. It is calculated as specified below, using the other 16 characters of the VIN.

A weight factor is assigned to all positions of the VIN, except of course to the 9th position (the check digit itself), as follows: 1=8, 2=7, 3=6, 4=5, 5=4, 6=3, 7=2, 8=10, 10=9, 11=8, 12=7, 13=6, 14=5, 15=4, 16=3, 17=2

The numerical values of the letters in the VIN are multiplied by their assigned weight factor.

The resulting products from step 3 are added up.

The sum of the products is divided by 11. The numerical remainder is the check digit. If the remainder is 10, the check digit is the letter X. So the 9th position of the VIN will be a number 0-9 or the letter X.

Example Check Digit calculation

Sum of all products = 277
277 / 11 = 25 with a remainder of 2, so the check digit is 2.
The full VIN is then JH4NA1152MT001365

Digits 1-3: Manufacturer & Make

J = Japan
H =  Honda Motor Co., LTD - Acura
4 = Passenger car (gasoline engine)

Digits 4-6: Model & Engine

NA1 = NSX 2 DR - 3.0L
NA2 = NSX 2 DR - 3.2L

Digit 7: Body & Transmission Type

1 = 2 DR Coupe - Manual
2 = 2 DR Coupe - Auto

Digit 8: Trim Level/Restraint System

2 = 1999 Zanardi Edition (Coupe with Manual Steering, Dual Airbag, Active Belt)
3 = 1997+ NSX Coupe with Power Steering, Dual Airbag, Active Belt
5 = 1991-1995 NSX Coupe with Manual Steering, Driver Airbag, Active Belt
6 = 1997+ NSX-T with Power Steering, Driver Airbag, Active Belt
8 = 1995-1996 NSX-T with Power Steering, Dual Airbags, Active Belt

Digit 9: Check Digit

0-9 or X

Digit 10: Model Year

M = 1991
N = 1992
P = 1993
R = 1994
S = 1995
T = 1996
V = 1997
W = 1998
X = 1999
Y = 2000
1 = 2001, 2 = 2002 . . . 9 = 2009
A = 2010 (the cycle repeats itself starting with A again)

They skip letters like "I", "O", and "Q" which could be confused with numeric digits.  The 10th digit of the VIN number is an industry standard.

Digit 11: Assembly Plant

T = Tochigi, Japan

Digit 12-17

Five Digit Sequential Serial Number - Starts at 000001 at the beginning of every model year.

Example

VIN # JH4NA1152MT001365 translates as:

J=Japan
H=Honda Motor Co., LTD-Acura
4=Passenger Car with Gasoline Engine
NA1=NSX 2 DR - 3.0L
1=2 Door Coupe - Manual
5=NSX, Manual Steering, Driver Airbag, Active Belt
2=Check Digit
M=1991 Model Year
T=Tochigi, Japan
001365=Sequential Serial Number

VIN Notes

For the US VIN numbers, the first 1991 car available for sale was 000063; all lower numbers were pre-production prototypes.

Cars sold outside the US have slightly different VIN number formats.  For example, NSX's built for the Canadian market have their own sequence number range, starting with 800001 each year.