The diagnostic trouble codes on a Subaru Impreza are relatively easy to check. These codes and the on-board diagnostic system as a whole are interconnected with your Subaru's service warning light on the dashboard, behind the steering wheel. If the light is not lit, then you likely do not have a pressing need to access the diagnostic system. However, dash bulbs can and do burn out, and if you think you have a problem, it's best to check. All you need is a diagnostic scanner fluent in OBD-II codes. Buying a scanner will pay for itself over the years.
Ensure that the engine is turned all the way off, including the electrical components.
Locate the Subaru's OBD-II diagnostic jack. It should be in the front of the car and in plain view. Law requires that this jack require no tools for access. In most models of most cars sold in the United States, the jack is located beneath the dashboard and steering wheel on the driver side of the car.
Connect the scanner to the jack. The scanner features an electrical cable with a wide, multiple-pin plug that should easily slide into place with a firm push.
Boot up the scanner and wait a few seconds for it to become fully operational.
Turn on the Sabaru and wait for the car to establish a working connection with the OBD-II scanner. This should take only a few seconds.
Look at the scanner's read-out screen. If there is a diagnostic trouble code in the Subaru's computer, it should display at this time. If the Subaru's diagnostic system has not found a problem, then no trouble code should appear.
