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On-Board Diagnostics – OBDII

Frequently Asked Questions About On-Board Diagnostics – OBDII

The Environmental Protection Agency has regulations in place establishing requirements for on-board diagnostics EPA LOGO On-board diagnostics - OBDII Brown's Alignment – OBDII systems on light-duty vehicles and light-duty trucks. This system began with the 1996 model year. The purpose of the OBDII system is to assure proper emission control system operation for the vehicle’s lifetime. This is done by monitoring emission related components and systems for deterioration and malfunction.

What Is On-Board Diagnostics – OBDII And How Does It Work?

By the early 1980’s, many vehicles were using electronics and On-board computers to control many of the engine’s control systems Mainly fuel and ignition systems. Vehicle manufacturers had to develop ways to diagnose problems generated by the new electronic hardware found under the hood. Thus, the first On-board diagnostics systems were developed by auto manufacturers in the early 1980. Electronic systems began to replaced mechanical systems. The first system was OBDI and each manufacturer developed their own system requiring a variety of diagnostic software and hardware.

The engines in today’s vehicles are largely electronically controlled. Sensors and actuators sense the operation of specific components. Oxygen sensors  and actuators  (e.g., the fuel injectors) are used to maintain optimal engine control. An on-board diagnostics – OBDII computer, known sometimes as a “powertrain control module” PCM or an “engine control module,” ECM controls all of these systems. With proper software, the on-board diagnostics 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 drivability. The sensors ‘and actuators, along with the diagnostic software in the on-board computer, make up what is called “the OBDII system.” On-board diagnostics – OBDII began in all vehicles in 1996 and created a standardized common diagnostic link connector and software for monitoring fuel and emission systems.

What Is The Connection Between On-board Diagnostics – OBDII And Vehicle Emissions?

There are circumstances under which the vehicle computer will detect a system problem before the driver notices a drivability problem. Furthermore, OBDII can detect problems that may not be noticeable upon visual inspection because many component failures that impact 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, EPA hopes that vehicles will be properly repaired before emissions become a problem.

How Does On board diagnostics – OBDII Inform Drivers Of Problems?

When the on-board diagnostic – OBDII system determines that a I problem exists. A corresponding “Diagnostic Trouble Code”  DTC is stored in the computer’s memory. The computer also illuminates a dashboard light indicating “Service Engine Soon” or “Check Engine” or displays an engine symbol. This light, usually yellow in color and serves to inform the driver that a problem has been detected. Vehicle service is needed. When the car is delivered to our auto repair shop our service technician can quickly retrieve the stored diagnostic trouble codes from the computer.  The diagnostic trouble codes will specify which system is malfunctioning. With this information the service technician can more quickly and accurately make the proper diagnosis and repair.

It is important to note that an illuminated dashboard light, as described here, is intended to inform the driver of the need for service, NOT of the need to stop the vehicle. However, service should be sought as soon as possible.

Why Does The Dashboard Light Blink Or Flash?

Under certain conditions, the dashboard light will blink or flash. The dash light is controlled by the on-board diagnostics – OBDII computer. This indicates a rather severe level of engine misfire. When this occurs, the driver should reduce speed and seek service as soon as possible. Severe engine misfire over only a short period of time can seriously damage emission control system components, especially the catalytic converter, which is typically the most expensive to replace. Drivers should also consult their vehicle owner’s manual for manufacturer specific information.