Equus 3110 - CanOBD2 Diagnostic Tool - Manual (Page 18)

16 CAN OBD2
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Onboard Diagnostics
COMPUTER ENGINE CONTROLS
The computer compares the values received from these sensors with
its preset reference values, and makes corrective actions as needed
so that the sensor values always match the preset reference values for
the current driving condition. The computer makes adjustments by
commanding other devices such as the fuel injectors, idle air control,
EGR valve or Ignition Module to perform these actions.
Vehicle operating conditions are constantly changing. The computer
continuously makes adjustments or corrections (especially to the
air/fuel mixture and spark timing) to keep all the engine systems oper-
ating within the preset reference values.
On-Board Diagnostics - First Generation (OBD 1)
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 pro-
gram would be capable of identifying emissions-related faults
in a system. The first generation of Onboard Diagnostics
came to be known as OBD 1.
OBD 1 is a set of self-testing and diagnostic instructions pro-
grammed into the vehicle’s on-board computer. The programs are
specifically 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 sys-
tems, it lights an indicator on the dashboard to alert the driver. The indi-
cator 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 “Scan Tool.”
With the exception of some 1994 and 1995 vehicles,
most vehicles from 1982 to 1995 are equipped with
some type of first generation On-Board Diagnostics.