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•
To standardize communication procedures and protocols between the
diagnostic equipment (Diagnostic Tools, Code Readers, etc.) and the
vehicle’s on-board computer.
2.3 diagnostic Trouble Codes (dTCs)
OBD II Diagnostic Trouble Codes are codes that are stored by the on-board
computer diagnostic system in response to a problem found in the vehicle.
These codes identify a particular problem area and are intended to provide
you with a guide as to where a fault might be occurring within a vehicle.
do
noT
replace parts based only on DTCs without first consulting the vehicle’s
service manual for proper testing procedures for that particular system, circuit
or component.
OBD II Diagnostic Trouble Codes consist of a five-digit alphanumeric code.
•
The 1st character is a
letter
(B, C, P or U). It identifies the “main system”
where the fault occurred (Body, Chassis, Powertrain, or Network).
•
The 2nd character is a
numeric digit
(0 thru 3). It identifies the “type” of
code (Generic or Manufacturer-Specific).
Generic DTCs are codes that are used by all vehicle manufacturers. The
standards for generic DTCs, as well as their definitions, are set by the Society of
Automotive Engineers (SAE).
Manufacturer-Specific DTCs are codes that are controlled by the vehicle
manufacturers. The Federal Government does not require vehicle
manufacturers to go beyond the standardized generic DTCs in order to comply
with the new OBD II emissions standards. However, manufacturers are free
to expand beyond the standardized codes to make their systems easier to
diagnose.
•
The 3rd character is a letter or a
numeric digit
(0 thru 9, A thru F). It
identifies the specific system or sub-system where the problem is located.
•
The 4th and 5th characters are
letters
or
numeric digits
(0 thru 9, A thru
F). They identify the section of the system that is malfunctioning.
showed the following:
•
A large number of vehicles had deteriorating or degraded emissions-related
components. These components were causing an increase in emissions.
•
Because OBD I 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 (OBD II/OBD 2).” The primary objective
of the OBD II system is to comply with the latest regulations and emissions
standards established by CARB and the EPA.
The Main Objectives of the OBD II 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 OBD II, DLCs were of different shapes and sizes.)
• To standardize the code numbers, code definitions and language used to
describe faults. (Before OBD II, 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).
Summary of Contents for CRT511
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