Since 1996, all Mazda models come outfitted with a system diagnostic controller with a data link connector (DLC). The DLC alerts the driver that there is a problem with the car through an engine warning light. An OBD II reader can be attached to the DLC to read the fault codes that the system diagnostic controller provides. These fault codes each represent a different problem with the vehicle. Many OBD II readers can also clear the fault codes, resetting the system diagnostic controller.
Locate the DLC on the Mazda. The DLC is located just under the dashboard in the driver side area but varies in exact placement. Specifics about the location, usually with a picture, can be found on the DLC locator link in the article Resources.
Turn the ignition key to the "On" position. The Mazda does not need to be started.
Connect the OBD II reader's connector to the DLC.
Follow the OBD II reader's instructions to erase existing fault codes. Different readers will have different methods of clearing fault codes, from pressing an "Erase Codes" button to going through menu options. This step will reset the system diagnostic controller, clearing all fault codes.
Disconnect the OBD II reader from the DLC after the reader has indicated that the clearing-fault-code process has been completed.
Start the Mazda and verify the check engine light is no longer lit. If still lit, repeat the above steps. If the check engine light stays lit after repeating the steps, this indicates a problem with the system diagnostic controller.
Many auto parts stores and automotive shops will plug their OBD II reader into your vehicle, provide the fault codes and reset the system diagnostic controller for free.