Craftsman 14063 manual On-Board Diagnostics First Generation OBD1

The OBD2 System is

an enhancement of the

OBD1 System.

Onboard Diagnostics

COMPUTER ENGINE CONTROLS

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 operating within the preset reference values.

On-Board Diagnostics - First Generation (OBD1)

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.

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

OBD1.

OBD1 is a set of self-testing and diagnostic instructions programmed 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 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 “Scan Tool.”

On-Board Diagnostics - Second Generation (OBD2)

In addition to performing all the functions of the OBD1 System, the OBD2 System has been enhanced with new Diagnostic Programs. These programs closely monitor the functions of various emissions-related compo- nents 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 OBD1 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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