OBD II Background

OBD-II




Beginning with the 1996 model year, all Volkswagen passenger vehicles are equipped to meet the new OBD-II diagnostic standard. OBD-II is a refinement of the older OBD-I standard. These new standards encompass more than engine operating parameters alone. Additional engine management components, engine and fuel systems, and non-engine systems are monitored as part of the OBD-II system.

OBD-II standards include:
^ Standardized diagnostic connection and location in the driver's area
^ Standardized DTCs for all manufacturers
^ Retrieval of DTCs by commercially available diagnostic equipment (generic scan tools)
^ Retention of operating conditions present during a monitored malfunction
^ Standards governing when and how a monitored malfunction must be displayed
^ Standardized names for components and systems

After establishing the set of standards as a framework, a set of objectives was developed to provide the basis for system operation.

The objectives include:
^ Operational monitoring of all components that have an influencing effect on exhaust emissions
^ Protection for the catalytic converter(s)
^ Visual display within driver's view (malfunction indicator light) to signal malfunctions in emissions-relevant components
^ On-board fault memory to store standardized error codes
^ Diagnosis capability

With the objectives firmly established, a clear method of achieving them was designed into the engine management system and the ECM. The monitored components and systems include:
^ Three-way catalytic converter
^ Oxygen sensors
^ Engine misfire detection
^ Secondary air injection
^ Exhaust gas recirculation
^ Evaporative emissions control and system integrity
^ Fuel distribution system
^ All sensors, components, and inputs associated with the ECM
^ Automatic transmission (emissions-related functions)

Summary

OBD-II systems are basically enhanced and expanded versions of OBD-I systems. Additional parts of the engine as well as other related systems and functions are included in the diagnostic structure. In practice, most of the changes are software changes to the ECM rather than major hardware changes. The new components simply provide more data to take advantage of the new computing power resulting in a dramatic reduction in total vehicle emissions.