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OBD II
In 1994, manufacturers began equipping vehicles with a new class of computer
technology which puts more processing power in the vehicle than ever before. It
is called On-Board Diagnostics, Second Generation (OBD II) and offers increased
system monitoring and diagnostic information. Beginning January 1, 1996,
vehicles sold in the U.S. are required to be OBD II compliant. However, a few
vehicles were exempt since no changes were made to the engine. Most domestic
manufacturers began using this system on some vehicles beginning as early as
1994.
OBD II systems are designed to meet or exceed standards and regulations to
improve air quality. These standards and regulations are primarily set forth by the
Environmental Protection Agency (EPA) Clean Air Act of 1990. Most of the
standards and regulations were developed by the California Air Resources Board
(CARB). OBD II systems are unique in that they possess the capability of
monitoring the performance of emission related systems and their components;
to detect hard and intermittent faults that may cause a vehicle to pollute.
This new system stores a large library of general trouble codes along with
manufacturer-specific codes, some of which can be accessed with the tool. These
codes cover:
B-Codes . . . . . . . Body Systems
C-Codes . . . . . Chassis Systems
Now, basic terms are standardized and all generic (global) codes share a common
format and terminology established by the manufacturers and the Society of
Automotive Engineers (SAE).
Basics of Computer-Controlled Vehicles
This section explains the engine computer control system, the types of sensors
and how the computer controls engine fuel delivery, idle speed and timing.
Additional information may be found in technical support books at your local library
or auto parts store. The more you know about the computer system, the better
you can diagnose vehicle computer problems.
Computer controls were originally installed on vehicles to meet federal government
regulations for lower emissions levels and improved fuel economy. This began in
the early 1980's when basic mechanical systems were no longer able to accurately
control key engine parameters. A computer could be programmed to control the
engine under various operating conditions, making the engine more reliable. While
these early systems were very limited in the scope of their control, providing only
10 to 14 trouble codes, they did help guide the vehicle repair process.
Today, computer controls have made cars and trucks faster, cleaner, and more
efficient than ever before.
B-1
U-Codes . Network Communications
P-Codes . . . . . . Powertrain Systems
About OBD II
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