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Automotive Diagnostic Connectors, Adapters, and Parts

All vehicles come with built-in computers that measure and record information about their various systems. This data is used by professionals to get a better idea of your car's overall condition in order to perform appropriate maintenance, diagnose problems, and make repairs. To collect this information for yourself, you're going to need a compatible adapter to connect your vehicle to your automotive diagnostic equipment.

How is diagnostic information read on vehicles?

To read information about your vehicle, you must connect a computer or device to the on-board diagnostics computer system. The on-board diagnostics system, or OBD, will provide you with various types of data to make repairs. Depending on your particular scanning tool, it may display the information in codes, graphs, or numerical data. Adapters allow you to connect to your specific device. One end is equipped with your vehicle's proprietary connector, while the other end connects to the scanning tool.

What types of vehicle adapters and connectors are available?

On-board diagnostics use a number of protocols. Some cars utilize a standard protocol, while other models can vary based on the manufacturer. Adapters can be used to transfer information through incompatible connectors so that you don't have to get a new scanning device.

  • ALDL: Also known as an Assembly Line Diagnostic Link, this connector is used on General Motors vehicles that were manufactured prior to standardization. They have a square shape and 12 pins.
  • J1939: J-style connectors are utilized on larger vehicles. In addition to diagnostic repair information, the round connection hub is used for communications. While J1939 connectors are the most common, there are a number of models available.
  • Round connectors: Round connectors were used on vehicles before automotive manufacturers adopted a standard. They can come in six- or nine-pin configurations.
  • Proprietary OBD-I: These are proprietary cables with shapes that are unique to the manufacturer. Most contain 12 pins, but some can include seven.
  • OBD-II: This became the standard in 1996. There are two types. Both are D-shaped connectors with 16 pins. However, type-A connectors have a long raised peg in the middle, while type-B connectors have two shorter pegs.
How do you access the on-board diagnostics port?

The automotive OBD system plugin is placed in the interior of your car. Most often, it's located on the driver's dashboard. To access it, you may need to move the driver's seat as far back as it can go and feel for the connector with your fingers. Here are some of the most common locations.

  • Below the steering column: Most automotive manufacturers place the connection point just underneath the dashboard trim. It may be located directly underneath the steering wheel, on the left side next to the door, or above the gas pedal.
  • Behind an access door: Some cars have a flush panel on the left side of the dashboard that's only used during maintenance. Pulling on the panel will release the door and reveal the connection point.
  • Glove box compartment: The connection point may be in the back of the compartment on some vehicles.
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