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On-Board Diagnostics: First (OBD1) and Second (OBD2) Generation

Published on December 26th, 2023

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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 onboard 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 onboard 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)

The OBD2 System is an enhancement of the OBD1 System.

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 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 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.
  • Because OBD1 systems only detect failed components, the degraded components were not setting codes.
  • Some emissions problems related to degraded components only occur when the vehicle is being driven under a load. The emission checks being conducted at the time were not performed under simulated driving conditions. As a result, a significant number of vehicles with degraded components were passing Emissions Tests.
  • Codes, code definitions, diagnostic connectors, communication protocols, and emissions terminology were different for each manufacturer. This caused confusion for the technicians working on different makes and models of vehicles.

To address the problems made evident by this study, CARB, and the EPA passed new laws and standardization requirements. These laws required vehicle manufacturers to equip their new vehicles with devices capable of meeting all of the new emissions standards and regulations. It was also decided that an enhanced onboard diagnostic system, capable of addressing all of these problems, was needed. This new system is known as On-Board Diagnostics Generation Two (OBD2). The primary objective of the OBD2 system is to comply with the latest regulations and emissions standards established by CARB and the EPA.

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The Main Objectives of the OBD2 System are:

  • To detect degraded and/or failed emissions-related components or systems that could cause tailpipe emissions to exceed by 1.5 times the Federal Test Procedure (FTP) standard.
  • To expand emissions-related system monitoring. This includes a set of computer-run diagnostics called Monitors. Monitors perform diagnostics and testing to verify that all emissions-related components and/or systems are operating correctly and within the manufacturer’s specifications.
  • To use a standardized Diagnostic Link Connector (DLC) in all vehicles. (Before OBD2, DLCs were of different shapes and sizes.)
  • To standardize the code numbers, code definitions, and language used to describe faults. (Before OBD2, each vehicle manufacturer used their own code numbers, code definitions, and language to describe the same faults.)
  • To expand the operation of the Malfunction Indicator Lamp (MIL).
  • To standardize communication procedures and protocols between the diagnostic equipment (Scan Tools, Code Readers, etc.) and the vehicle’s onboard computer.

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