Your car’s vehicle identification number, or VIN, is your car’s fingerprint, DNA and Social Security number all rolled into one.

The number has always been important when buying a used car as a way to track a car’s history before purchase. Now, it’s important for new car deals, too.

In some instances, readers are reporting that dealerships have asked them to sign a corrected contract on a new car purchase after it was discovered the initial paperwork carried the wrong VIN number.

Where do you find the VIN? It’s the string of letters and numbers mounted on the driver’s side of the dashboard at the bottom of the windshield. No two VINs are alike. Those 17 numbers and letters spell out just about all there is to know about your vehicle.

Its code represents the country where the vehicle was built, the manufacturer, the body style, the model year, the specific factory where it was assembled and a number for your specific vehicle as it rolled off the production line, says Ian Hamilton, president of Vinguard, a Canadian company that sells theft-deterrent kits for etching a VIN number on a car window.

As simple as it sounds, when you buy or lease a car, it’s a good idea to double-check — while you’re still at the dealership — that the VIN on your paperwork matches the car’s VIN.

If it doesn’t, that can cause headaches. Besides being listed on your loan or lease agreement, your VIN is used to identify your car on the title, insurance and registration, as well as in accident records. The VIN stays with your car throughout its life.

Getting the VIN wrong is a serious mistake. It’s the automotive equivalent of accidentally switching babies at the hospital. But what’s really troubling is if the dealership asks the customer to sign a new contract for more money based on the right VIN.

That’s a big red flag, says attorney Tom Hudson, a partner with Hudson Cook LLP, a law firm in Hanover, Md., which represents car dealerships, auto lenders and other automotive service providers. “A reputable dealer has no business asking for a new contract with a higher payment,” he says.

Hudson says if the dealership says it accidentally got the VIN wrong, the first thing you should do is double-check the numbers on your vehicle. Compare the VIN in the car to the number on your finance contract. It may also appear on your monthly bill from the lender.

In the event there’s been an honest mistake, it may be possible to write and initial changes on your original contract rather than write a whole new contract, Hudson says. But you or the dealership also must fix the other records that have the wrong VIN.

If a dealership demands more money than was initially negotiated, complain to the dealership’s owner, not just the finance manager. You can also call the lender, and explain that the dealership got the VIN wrong and is now asking for more money. That really shouldn’t happen.

As a last step, you can complain to your state attorney general’s office or consumer-affairs office. Hopefully, it won’t reach that stage.