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3
DN606 Automotive Diagnostic Tool User's Manual
2. General Information
2.1 On-Board Diagnostics (OBD) I
Note: With the exception of some 1994 and 1995 vehicles, most vehicles from
1982 to 1995 are equipped with some type of rst generation On-Board Diagnostics.
Beginning in 1988, California’s Air Resources Board (CARB), and later the
Environmental Protection Agency (EPA) required vehicle manufacturers to
include a self-diagnostic program in their on-board computers. The program
would be capable of identifying emissions-related faults in a system. The first
generation of Onboard Diagnostics came to be known as OBD I.
OBD I is a set of self-testing and diagnostic instructions programmed into the
vehicle’s onboard computer. The programs are specically designed to detect
failures in the sensors, actuators, switches and wiring of the various vehicle
emissions-related systems. If the computer detects a failure in any of these
components or systems, it lights an indicator on the dashboard to alert the driver.
The indicator lights only when an emissions-related problem is detected.
The computer also assigns a numeric code for each specific problem that it
detects, and stores these codes in its memory for later retrieval. These codes
can be retrieved from the computer’s memory with the use of a “Code Reader”
or a “Diagnostic Tool.”
2.2 On-Board Diagnostics (OBD) II
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”.
In addition to performing all the functions of the OBD I System, the OBD II
System has been enhanced with new Diagnostic Programs. These programs
closely monitor the functions of various emissions-related components and
systems (as well as other systems) and make this information readily available
(with the proper equipment) to the technician for evaluation.
The California Air Resources Board (CARB) conducted studies on OBD I
equipped vehicles. The information that was gathered from these studies
showed the following:
• A large number of vehicles had deteriorating or degraded emissions-related
components. These components were causing an increase in emissions.
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