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Onboard Diagnostics
COMPUTER ENGINE CONTROLS
Craftsman 14063 11
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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 make and model vehicles.
To address the problems made evident by this study, CARB and the
EPA passed new laws and standardization requirements. These laws
required that 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 on-board 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.
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 on-board computer.
OBD2 Terminology
The following terms and their definitions are related to OBD2 systems.
Read and reference this list as needed to aid in the understanding of
OBD2 systems.