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1.0 General Information: On-Board Diagnostics (OBD) II
The first generation of On-Board Diagnostics (called OBD I) was developed by the California Air Resources Board (ARB) and
implemented in 1988 to monitor some of the emission control components on vehicles. As technology evolved and the desire to
improve the On-Board Diagnostic system increased, a new generation of On-Board Diagnostic system was developed. This
second generation of On-Board Diagnostic regulations is called “OBD II”.
The OBD II system is designed to monitor emission control systems and key engine components by performing either
continuous or periodic tests of specific components and vehicle conditions. When a problem is detected, the OBD II system
turns on a warning lamp (MIL) on the vehicle instrument
panel to alert the driver typically by the phrase of “Check Engine” or “Service Engine Soon”. The system will also store
important information about the detected malfunction so that a technician can accurately find and fix the problem. Here below
follow three pieces of such valuable information:
1) Whether the Malfunction Indicator Light (MIL) is commanded ‘on’ or ‘off’;
2) Which, if any, Diagnostic Trouble Codes (DTCs) are stored;
3) Readiness Monitor status.
1.1 Location of the Data Link Connector (DLC)
The DLC (Data Link Connector or Diagnostic Link Connector) is the standardized 16-cavity connector where diagnostic
scan tools interface with the vehicle’ s on-board computer. The DLC is usually located 12 inches from the center of the
instrument panel (dash), under or around the driver ’ s side for most vehicles, IF Data Link Connector is not located under
dashboard, a label should be there telling location, For some Asian and European vehicles, the DLC is located behind the
ashtray and the ashtray must be removed to access the connect If the DLC cannot be found, refer to the vehicle’s service
manual for the location.
1.2 Diagnostic Trouble Codes (DTCs)
OBD II Diagnostic Trouble Codes are codes that are stored by the on—board computer diagnostic system in
response to a problem found in the vehicle, These codes identify a particular problem area and are intended to provide
you with a guide as to where a fault might be occurring within a vehicle. OBD II Diagnostic Trouble Codes consist of a
five-digit alphanumeric code, The first character, a letter, identifies which control system sets the code, The other four
characters, all numbers, provide additional information on where the DTC originated and the operating conditions that
caused it to set, Here below is an example to illustrate the structure of the digits:
Identifying specific malfunctioning section of the systems.
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