First, the vehicle is checked to see if the Malfunction Indicator Light (commonly called the "check engine" or "service engine soon" light) on the instrument panel illuminates when the ignition key is turned to the "on" position and then when the engine is running. Next, an electronic device known as a scan tool is connected to the vehicle, and used to communicate with the vehicle’s on board computer. The on board computer is checked to confirm that the vehicle is ready to be tested, to determine if the computer has attempted to turn on the Malfunction Indicator Light, and if applicable, to retrieve diagnostic trouble codes. The results are recorded, and the scan tool is disconnected from the vehicle. The entire OBD check typically takes less than 5 minutes.
Agency of Transportation