On-board diagnostics

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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 a repair technician access to the status of the various vehicle subsystems. The amount of diagnostic information available via OBD has varied widely since its introduction in the early 1980s. Early versions of OBD would simply illuminate a malfunction indicator light (MIL) 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 (DTCs), which allow one to rapidly identify and remedy malfunctions within the vehicle.

History

The history of OBD can be traced back to the introduction of the California Air Resources Board (CARB) regulations in the 1980s. The first OBD systems were developed to monitor emissions control systems. The OBD-I standard was introduced in 1988, which required vehicles to have a basic level of diagnostic capability. The more advanced OBD-II standard was introduced in 1996, which provided a more comprehensive set of diagnostics and a standardized connector and communication protocol.

OBD-I

OBD-I was the first generation of on-board self-diagnostic equipment. It was introduced in the late 1980s and was primarily used to monitor emissions control systems. OBD-I systems were not standardized, and each manufacturer had its own set of diagnostic trouble codes and communication protocols.

OBD-II

OBD-II is the second generation of on-board diagnostics and was introduced in 1996. It provides a standardized hardware interface—the 16-pin (2x8) J1962 connector, which is usually located on the driver's side of the vehicle. OBD-II also provides a standardized set of diagnostic trouble codes (DTCs) and a standardized communication protocol. The OBD-II standard specifies the type of diagnostic connector and its pinout, the electrical signaling protocols available, and the messaging format. It also provides a list of vehicle parameters to monitor along with how to encode the data for each.

Diagnostic Trouble Codes (DTCs)

Diagnostic Trouble Codes (DTCs) are codes that the OBD system uses to identify a particular problem area in the vehicle. Each DTC consists of a five-character alphanumeric code. The first character is a letter that indicates the system related to the trouble code (e.g., P for powertrain, B for body, C for chassis, and U for network). The remaining characters are numbers that provide more specific information about the problem.

OBD-II Protocols

OBD-II defines several communication protocols that are used to transmit data between the vehicle's OBD system and a diagnostic tool. These protocols include:

• SAE J1850 PWM (Pulse Width Modulation)
• SAE J1850 VPW (Variable Pulse Width)
• ISO 9141-2
• ISO 14230 KWP2000 (Keyword Protocol 2000)
• ISO 15765 CAN (Controller Area Network)

Applications

OBD systems are used for a variety of applications, including:

• Emissions testing and control
• Monitoring vehicle performance
• Diagnosing and repairing vehicle malfunctions
• Providing data for telematics and fleet management systems

See also

• Emission standard
• Check engine light
• Vehicle emissions control
• Automotive diagnostic tools
• Telematics