2. General Information
2.1 On-Board Diagnostics（OBD）II
The first generation of On-Board Diagnostics(calle 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 eigher 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 follow
three pices 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.
2.2 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
consists 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:
2
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