OBD is the abbreviation of On-Board Diagnostics, which is an online monitor diagnosis system mainly controlling vehicle emission; meanwhile, it also monitors other engine related fault. The system will timely monitor whether the vehicle exhaust exceeds the standard according to the operation condition of the engine; or else, it will immediately issue a warning. In case of system fault, OBD (MIL) lamp or service diagnosis (Service) lamp is on, the fault diagnosis management system (DSM) will store the fault information in the memory; the fault code can be read out from DSM via a certain program. According to the prompt of fault code, the maintenance personnel can rapidly and accurately determine the nature and location of fault code.