OBD-II Subaru Diagnostic Systems:

With proper software, the on-board computer is capable of monitoring all of the sensors and actuators to determine whether they are working as intended. It can detect a malfunction or deterioration of the various sensors and actuators, usually well before the driver becomes aware of the problem through a loss in vehicle performance or driveability. The sensors and actuators, along with the diagnostic software in the on-board computer, make up what is called “the OBD-II system.”

The purpose of the OBD-II system is to assure proper emission control system operation for the vehicle’s lifetime by monitoring emission-related components and systems for deterioration and malfunction. There are circumstances under which the vehicle computer will detect a system problem before the driver notices a drive-ability problem.

Furthermore, OBD-II can detect problems that may not be noticeable upon visual inspection because many component failures that have an effect on emissions can be electrical or even chemical in nature. By detecting these emission-related failures and alerting the driver to the need for potential repair, vehicles can be properly repaired before emissions become a problem.

When the OBD-II system determines that a problem exists, a corresponding Diagnostic Trouble Code (DTC) is stored in the computer’s memory. The computer also illuminates a dashboard CHECK ENGINE light. This light serves to inform the driver that a problem has been detected and vehicle service is needed. When the car is delivered to the repair shop, a service technician can quickly retrieve the stored diagnostic trouble codes from the computer memory of the vehicle using newly developed diagnostic tools. Since the diagnostic trouble codes will specifically identify the problem, the service technician can more quickly and accurately make the proper repair.