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  • On-board diagnostics


    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 subsystems. 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.

  • Idiot light


    A group of tell-tales Graphical tell-tales An idiot light, sometimes "tell-tale" or "warning light", is an indicator of malfunction of a system, indicated by a binary (on/off) illuminated light, symbol or text legend. The "idiot light" terminology arises from popular frustration with automakers' use of lights for crucial functions which could previously be monitored by gauges, so a troublesome condition could be detected and corrected early. Such early detection of problems with, for example, engine temperature or oil pressure or charging system operation is not possible via an idiot light, which lights only when a fault has already occurred – thus providing no advance warnings or details of the malfunction's extent. The Hudson automobile company was the first to use lights instead of gauges for oil pressure and the voltmeter, starting in the mid-1930s.

  • Check engine light


    Malfunction Indicator Icon A Malfunction Indicator Lamp, this one labeled "Service Engine Soon". A MIL "Check Engine" light on a Volkswagen Bora indicating a fault in the Engine Management System. MIL on a running engine indicating malfunction in engine control system. A malfunction indicator lamp (MIL), or check engine light, is a tell-tale that a computerized engine-management system uses to indicate a malfunction. Found on the instrument panel of most automobiles, it usually bears the legend , , or a pictogram of an engine - and when illuminated it is typically either an amber or red color. The light generally has two stages: steady (indicating a minor fault) and flashing (indicating a severe fault). When the MIL is lit, the engine control unit stores a fault code related to the malfunction, which can be retrieved - although in many models this requires the use of a scan tool. This warning light can indicate almost anything from a loose gas cap to a serious knock in the engine. In the United States, specific functions are required of the MIL by EPA regulations.

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