In the automotive context On-Board Diagnostics, or OBD refers to a vehicle's self-diagnostic and reporting capability and presents the vehicle owner or a repair technician with state of health information for various vehicle sub-systems. Earlier systems of OBD could simply illuminate a malfunction indicator light, or MIL, if a problem were detected--but the nature of the problem could not be specified.
But by the introduction of on-board vehicle computers in the early 1980's, which had made OBD possible the amount of diagnostic information available has had dramatic changes. Modern day systems gives diagnostic trouble codes, or DTCs, which allows one to rapidly identify and fix malfunctions within the vehicle and all this is possible due to the use of standardized fast digital communications port which provide abundant realtime data.
On-Board Diagnostics, or OBD, in an automotive context, is a generic term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since the introduction in the early 1980s of on-board vehicle computers, which made OBD possible. Early instances of OBD would simply illuminate a malfunction indicator light, or 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 fast digital communications port to provide realtime 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.
* 1975: Datsun 280z On-board computers begin appearing on consumer vehicles, largely motivated by their need for real-time tuning of fuel injection systems. Simple OBD implementations appear, though there is no standardization in what is monitored or how it is reported.
* 1982: General Motors implements a proprietary interface and protocol. The initial ALDL protocol communicates at 160 baud with Pulse-width modulation (PWM) signaling and monitors very few vehicle systems.
* 1986: An upgraded version of the ALDL protocol appears which communicates at 8192 baud with half-duplex UART signaling. This protocol is defined in GM XDE-5024B.
* ~1987: The California Air Resources Board (CARB) requires that all new vehicles sold in California starting in manufacturer's year 1988 (MY1988) have some basic OBD capability. The requirements they specify are generally referred to as the "OBD-I" standard, though this name is not applied until the introduction of OBD-II. The data link connector and its position are not standardized, nor is the data protocol.
* 1988: The Society of Automotive Engineers (SAE) recommends a standardized diagnostic connector and set of diagnostic test signals.
* ~1994: Motivated by a desire for a state-wide emissions testing program, the CARB issues the OBD-II specification and mandates that it be adopted for all cars sold in California starting in model year 1996 (see CCR Title 13 Section 1968.1 and 40 CFR Part 86 Section 86.094). The DTCs and connector suggested by the SAE are incorporated into this specification.
* 1996: The OBD-II specification is made mandatory for all cars sold in the United States.
* 2001: The European Union makes EOBD mandatory for all petrol vehicles sold in the European Union, starting in MY2001 (see European emission standards Directive 98/69/EC  ).
* 2008: All cars sold in the United States are required to use the ISO 15765-4  signaling standard (a variant of the Controller Area Network (CAN) bus).
OBD scan tools can be categorized in several ways ranging from whether they are OEM tools or aftermarket tools, whether they require a computer to operate (stand-alone tool vs PC-based software), and the intended market (professional or hobby/consumer use).
The advantages of PC-based scan tools are:
* Low cost (compared to stand-alone scan tools with similar functionality -if you don't count the cost of a laptop PC).
* Virtually unlimited storage capacity for data logging and other functions.
* Higher resolution screen than handheld tools.
* Availability of multiple software programs.
* Some are capable of reprogramming
The advantages of stand-alone tools:
* Wide selection beginning with simple code read/erase tools starting at as low as $79 retail.
* Simplified operation that requires no computer skills/ PC compatibility issues.
* Rugged designs, intended for use in and around cars (i.e. no lugging a laptop in and around a car).
See List of Standalone OBD-II Scan Tools, List of OBD-II Cables & Scanning Software, and List of OBD-II Gauges & Performance Monitors.