First, here is the definition of the Check Digit, paraphrased from the public National Highway Traffic Safety Administration (NHTSA) site, from their manufacturer handbook:
The VIN Check Digit consists of one character, which occupies Position 9 in the VIN. The check digit’s purpose is to provide a means for verifying the accuracy of any VIN transcription. NHTSA regulations establish a mathematical formula for calculating the check digit.
Once all of the other characters in VIN have been determined by the manufacturer, the check digit is calculated by carrying out the mathematical computation specified under NHTSA regulations.
If a user receives the message “Warning – This VIN does not pass check sum validation“, this indicates that the 9th position of the VIN does not match the result of the mathematical formula used to calculate the check digit using the entirety of the VIN.
The reasons for this could range from a typographical error in the VIN as entered or previously recorded, to an error within the actual VIN assigned to this vehicle by the manufacturer, as well as other errors.
The warning message is to inform the user of this discrepancy, however, an error in this position of the VIN will not affect vehicle valuation using our valuation applications. Questions regarding the validity of the VIN as it pertains to this error should be directed to the manufacturer of the vehicle for further review.