Do you know anyone who’s had a DNA ancestry blood test? Many people are surprised to learn that their genetic code includes ancestors from locations they never expected. Likewise, your car can have a global history, as increasingly, vehicle makers source the world for parts. Like your DNA, your vehicle’s identification number, or VIN, is unique to your car and can be decoded to provide information about its history and components, such as where the vehicle was built and what engine and transmission it was equipped with. Along with the VIN, your vehicle has other key identifiers, such as RPO codes, model, and serial numbers.

Imagine you’re an automaker and each year you build 50 models and each model has thousands of discrete parts from nuts and bolts to engines. Some of the models share parts and some were introduced mid-year, others are replacements because a part supplier had bad weather. Yet, all must work together in order for the vehicle to function properly. How to keep track of it all? Part of the answer is VIN codes.

The Vehicle Identification Number (VIN) is a 17-digit combination of letters and numbers. Carmakers stamp the VIN on a metal tab riveted on the instrument panel, top upper left of the dash. (Courtesy Mazda)

When you're replacing parts, often you can use the VIN to select the correct replacement part. Since many parts can’t be returned after purchase, make sure to get all 17 digits of the VIN correctly, as just one incorrect digit makes a difference. TIP: Use a phone or camera to photograph the VIN. For late-model vehicles, the VIN is visible when outside looking in the driver’s window. For older vehicles, the owner's manual may show the VIN location. Often the VIN is printed on paperwork, such as the following:

  • auto insurance invoice or policy
  • proof of auto insurance card
  • car registration or title
  • vehicle certification label

Another use of the VIN is to check for recalls. Auto manufacturers "recall" vehicles when there is a critical or safety issue, asking car owners to return to the dealer for repairs at no charge. According to the National Highway Traffic Safety Administration (NHTSA), about 25% of recalls are not repaired. Driving an unrepaired recalled vehicle is potentially unsafe for you and for others on the road. There's a simple tool at Enter the VIN to see what recalls need to be repaired for the vehicle. Check your Chilton subscription for the full text of a recall bulletin.

Type 64 Rome to Berlin Racer

Most vehicle makers use other identifiers too, such as model codes and serial codes. Ferdinand Porsche used "Type codes” beginning with early Volkswagens, Audis (Auto Union and Wanderer), and Porsches. These codes help identify new models and prototypes, as well as specific components (such as brakes or engines) or packages (such as for competition).

General Motors uses “regular production option,” or RPO codes, to identify a component the vehicle is originally equipped with, such as fog lights, or a package, such as sport suspension. RPO codes are combinations of three numbers and letters, such as RPO T4A. The RPO code helps locate the replacement part the automaker designed to fit and work well on the vehicle.

Some RPO codes became famous, such as the Z28 (Camaro). Notable or not, General Motors reuses codes, such as the venerable Corvette ZR1. GM used ZR1 first from 1969 through 1970, and then again in the early 1990s, and a third time from 2009-2013. When GM reuses an RPO code it could be for the same vehicle or component, or for an entirely different one, as well as a different brand, or year, requiring more careful attention when replacing parts.

RPO and VIN codes tell what the vehicle was originally equipped with, so if it is an older vehicle, things may have changed!

Increasingly, GM service and repair procedures refer to RPO codes to identify the correct components and procedures. You’ll see these references in ChiltonDIY’s newer General Motors models (from 1998 onward, and some earlier) to assist you in identifying the specific components originally equipped on your vehicle. With ChiltonDIY as a reference, the building blocks of your vehicle's DNA, the VIN, RPO codes, and other identifiers will help you to select the correct replacement part to keep your vehicle running smoothly.