On-Board Diagnostics, in an automotive context, is a generic term referring to hardware diagnostic capability that is present in most cars and light trucks on the road today.
During the 1970s and early 1980s manufacturers started using electronic means to control engine functions and diagnose engine problems. This was primarily to meet EPA emission standards. Through the years on-board diagnostic systems have become more sophisticated.
OBD2
OBD2 is a standard interface to the on-board computer of a vehicle, introduced in the mid-1990s. The California Air Resources Board (CARB) mandated that the specification be adopted for all cars sold in the United States by the year 1996 in order to simplify the implementation of an emissions testing program. An OBD-II interface allows for the readout of DTCs (Diagnostic Trouble Codes) that have been generated by the on-board computer, as well as realtime data from the sensors connected to the on-board computer. In addition, the OBD-II interface provides a means to clear the DTC list once maintenance has been completed. For a list of generic OBD-II DTCs, see Table of OBD-II Codes. Individual manufactures have been known to enhance the OBD-II code set with a host of proprietary DTCs. The OBD-II specification provides for a standarized hardware interface—the female 16-pin (2?8) J1692 assembly. Unlike the OBD-I connector, which was found under the hood of the vehicle, the OBD-II connector is located on the driver’s side of the passenger compartment near the center console. Unfortunately, the OBD-II specification does not require a particular communication protocol be used on this interface. In general, only a few of the contacts on the J1692 are populated and the configuration of populated contacts can reveal the communication protocol used by the on-board computer. There are at least five protocols in use with the OBD-II interface:
* SAE J1850 PWM (41.6 kbaud, standard of the Ford Motor Company)
o pin 2 Data high
o pin 10 Data low
* SAE J1850 VPW (Variable pulse width) (10.4 kbaud, standard of General Motors)
o pin 2 Data
* ISO 9141 (RS-232 at non-standard voltages, used by numerous manufactures including most non-American cars)
o pin 7 Data K
o pin 15 Data L (this line optional in protocol, pin may not be populated in connector)
* ISO 14230 KWP2000 (Keyword Protocol 2000)
o pin 7 Data K
o pin 15 Data L (this line optional in protocol, pin may not be populated in connector)
* ISO 15765 CAN
o pin 6 Data high
o pin 14 Data low
Note that pins 5 (battery ground) and 16 (battery positive) are present in all configurations. Also, ISO 9141 and ISO 14230 use the same pinout, thus you cannot distinguish between the two simply by examining the connector. EOBD and JOBD
In Europe the EOBD (European On-Board Diagnostics) system was mandated by European Directive 98/69/EC for all petrol vehicles made from 1 January 2001. It is similar to the American OBD-II standard. In Japan, the JOBD system is used. CAN bus
Some newer cars (usually post-2003) also support the CAN bus, a local area network in some cars that also gives access to additional hardware like radios, navigation systems, and more. By 2008, all vehicles sold in the US must come equipped with CAN bus. CAN bus devices are usually connected to via the OBD2 connector.
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