Constant, the check digit is totally random with low volume manufacturers. The only reason I know anything about this, was that it was a major exercise to get the VIN decoded for my car and accepted by the authorities

Explanation:

The check digit for a VIN is obtained through a number of mathematical steps. Each letter used in a VIN has a corresponding number value, while numbers stay the same. Therefore, the VIN becomes a string of 17 numbers (with a space in the ninth position, where the check digit goes). Each position in the VIN has a weight - the number of times that digit is multiplied.

For example, the weight of position one is eight. A computer multiplies the number in position one is by 8. Then it multiplies all 16 numbers by the appropriate weight for their position in the VIN, adds the results together and divides that result by 11. The remainder becomes the check digit. If the remainder is 10, the check digit is X.

Example:

Using our theoretical VIN for AK1159 the check digit should be 4