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Ultrascan OBDCAN Series User's Manual
2 General Information
2.1 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.
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
consist of a five-digit alphanumeric code. The first character, a letter,
identifies which control system sets the code. The second character,
a number, 0-3; other three characters, a hex character, 0-9 or A-F
provide additional information on where the DTC originated and the
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