Development of the OBD
Due to the increase in pollutant levels in the air, more and more electronic components have been added to the car for the purpose of emission control. However, this has made error diagnosis in repair shops increasingly difficult. As a result, the on-board diagnostics (OBD) was introduced to provide assistance in the repair shops.
How the OBD works
If a fault occurs that compromises the exhaust gas quality, a standardised diagnostic trouble code is stored in the fault code memory of the engine control unit. The operating data and environmental conditions at the time the fault occurred are also stored.
If a fault relating to exhaust gas occurs, the OBD lamp (engine check lamp) will light up continuously. If a fault occurs that leads to cylinder shut-off or to damage of the catalytic converter, the OBD lamp will flash. Depending on the severity of the fault, limp-home programs may be activated to protect the engine. If a fault does not recur within a certain time period, the OBD lamp may go out again. The fault remains in the memory in any case. Faults and recorded data can be read out using a scan tool via the diagnostic socket. The diagnostic trouble code specifies the component in question and the type of fault. This makes them useful aids in diagnosing and resolving the fault.