According to Wikipedia,On-board diagnostics(OBD) is an?automotive?term referring to a vehicle’s self-diagnostic and reporting capability. OBD systems give the vehicle owner or repair technician access to the status of the various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since its introduction in the early 1980s’ versions of on-board vehicle computers. Early versions of OBD would simply illuminate a malfunction indicator light or “idiot light” if a problem was detected but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized digital communications port to provide real-time data in addition to a standardized series of?diagnostic trouble codes, or DTCs, which allow one to rapidly identify and remedy malfunctions within the vehicle.
OBD systems are exist in majority cars and light trucks on the road nowadays. During the 70’s and early 1980’s, manufacturers started using electronic means to control engine functions and diagnose engine problems. This was primarily to meet EPA emission standards. Through the years,OBD systems have become more sophisticated.
OBD-II, a new standard introduced in the mid 90’s, provides almost complete engine control and also monitors parts of the chassis, body and accessory devices, as well as the diagnostic control network of the car.
OBD-II is an improvement over OBD-I in both capability and standardization. The OBD-II standard specifies the type of diagnostic connector and its pinout, the electrical signalling protocols available, and the messaging format. It also provides a candidate list of vehicle parameters to monitor along with how to encode the data for each. There is a pin in the connector that provides power for the scan tool from the vehicle battery, which eliminates the need to connect a scan tool to a power source separately. However, some technicians might still connect the scan tool to an auxiliary power source to protect data in the unusual event that a vehicle experiences a loss of electrical power due to a malfunction. Finally, the OBD-II standard provides an extensible list of DTCs. As a result of this standardization, a single device can query the on-board computer(s) in any vehicle. This OBD-II came in two models OBD-IIA and OBD-IIB. OBD-II standardization was prompted by emissions requirements, and though only emission-related codes and data are required to be transmitted through it, most manufacturers have made the OBD-II?Data Link Connector?the only one in the vehicle through which all systems are diagnosed and programmed. OBD-II Diagnostic Trouble Codes are 4-digit, preceded by a letter: P for engine and transmission (powertrain), B for body, C for chassis, and U for network.
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