OBD II: On-Board Diagnosis - A (self-diagnosis) mechanism is provided by the DME III or DDE engine management system. Its purpose is to permit malfunctions tube identified before more serious damage results. Defects which occur suddenly, or values which go beyond the specified tolerance limits, are stored electronically and can be displayed and evaluated later on the screen of a diagnostic testing unit in the workshop. Troubleshooting then becomes much more straightforward and costs are reduced.