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 (CARB) 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 “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 other four characters, all numbers, provide
additional information on where the DTC originated and the operating
conditions that caused it to be set. Below is an example to illustrate the
structure of the digits:
3
