The OBD-II code reader is a type of universal automotive computer code reader. Before the 1990s, each individual automotive manufacturer had its own set of codes and code readers to use for independent diagnosis purposes. The OBD-II code reader works for all brands of cars, and can be found at virtually all mechanics shops and parts stores in the United States. It is the primary diagnostic tool used by automotive repair persons when diagnosing and repairing a problem on a vehicle. The OBD-II code reader is simple and effective to use.
Locate your car's computer. It is typically a black, plastic electronic box under the dashboard of your car. The specific location will vary slightly, so check your vehicle's owners manual to find out the precise location of the computer. It has an opening on one side where you can plug the cable of the OBD-II code reader into it.2
Turn the key in your vehicle to "on" and insert the plug end of your OBD-II code reader's cable into the receiver port on the computer. Make sure the check engine or other malfunction indicator lights are on; if they are not, you will not receive any codes because the car's computer has sensed a problem within the system. Press the button on your code reader to scan the computer. Some code readers will do this automatically, so read the instructions in your code reader's user manual to find out how your specific model operates before you use it so that you know what to expect.3
Make note of the codes that appear on the screen of your code reader. These are the error codes that are causing your car's malfunction indicator lights to come on when the computer senses a problem.4
Decode the error codes using the OBD-II code reader's user manual or a website such as Engine Light Help, which provides lists of error codes by both automobile manufacturer and generic code listings. Once you have decoded your error codes, you will have diagnosed the problem with your vehicle.