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Where'd
it come from?
Why do we
need it?
Does my
car have OBD-II?
How
do we measure OBD-II output?
What
good does it do to measure OBD-II output?
Tell
me about that "Check Engine Light".
OBD-II
and your car's health
Proprietary
Sensor Readings
OBD-II
and performance tuning
What
is OBD-II?
On-Board Diagnostic systems are in
most cars and light trucks on the road today. During the '70s
and early 1980's manufacturers started using electronic means
to control engine functions and diagnose engine problems. This
was primarily to meet EPA emission standards. Through the years
on-board diagnostic systems have become more sophisticated.
OBD-II, a new standard introduced in the mid-'90s, provides
almost complete engine control and also monitors parts of the
chassis, body and accessory devices, as well as the diagnostic
control network of the car.
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Where'd
it come from?
To combat its smog problem in the
LA basin, the State of California started requiring emission
control systems on 1966 model cars. The federal government extended
these controls nationwide in 1968.
Congress passed the Clean Air Act
in 1970 and established the Environmental Protection Agency
(EPA). This started a series of graduated emission standards
and requirements for maintenance of vehicles for extended periods
of time. To meet these standards, manufacturers turned to electronically
controlled fuel feed and ignition systems. Sensors measured
engine performance and adjusted the systems to provide minimum
pollution. These sensors were also accessed to provide early
diagnostic assistance.
At first there were few standards
and each manufacturer had their own systems and signals. In
1988, the Society of Automotive Engineers (SAE) set a standard
connector plug and set of diagnostic test signals. The EPA adapted
most of their standards from the SAE on-board diagnostic programs
and recommendations. OBD-II is an expanded set of standards
and practices developed by SAE and adopted by the EPA and CARB
(California Air Resources Board) for implementation by January
1, 1996.
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Why
do we need it?
The Environmental Protection Agency
has been charged with reducing "mobile emissions" from cars
and trucks and given the power to require manufacturers to build
cars which meet increasingly stiff emissions standards. The
manufacturers must further maintain the emission standards of
the cars for the useful life of the vehicle. OBD-II provides
a universal inspection and diagnosis method to be sure the car
is performing to OEM standards. While there is argument as to
the exact standards and methodology employed, the fact is there
is a need to reduce vehicle emitted pollution levels in our
cities, and we have to live with these requirements.
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Does
my car have OBD-II?
All cars built since January 1, 1996
have OBD-II systems. Manufacturers started incorporating OBD-II
in various models as early as 1994. Some early OBD-II cars were
not 100% compliant. <Click
here> to see the dates OBD-II started being included
on specific makes and models.
There are three basic OBD-II protocols
in use, each with minor variations on the communication pattern
between the on-board diagnostic computer and the scanner console
or tool. While there have been some manufacturer changes between
protocols in the past few years, as a rule of thumb, Chrysler
products and all European and most Asian imports use ISO 9141
circuitry. GM cars and light trucks use SAE J1850 VPW (Variable
Pulse Width Modulation), and Fords use SAE J1850 PWM (Pulse
Width Modulation) communication patterns. <Click
here> to see which cars use each system.
You may also tell which protocol
is used on a specific automobile by examining the connector
socket carefully. If the dash connector has a pin in the #7
position and no pin at #2 or #10, then the car has the ISO 9141
protocol. If no pin is present in the #7 position, the car uses
an SAE protocol. If there are pins in positions #7 and #2 and/or
#10, the car may use the ISO protocol.
While there are three OBD-II electrical
connection protocols, the command set is fixed according to
the SAE J1979 standard.
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How
do we measure OBD-II output?
Pre-OBD-II cars had connectors in
various positions under the dashboard and under the hood. All
OBD-II cars have a connector located in the passenger compartment
easily accessible from the driver's seat. Check under the dash
or behind or near the ashtray. A cable is plugged into the OBD-II
J1962 connector and connected to AutoTap or another scan tool.
AutoTap is available in PC/laptop or a Palm PDA versions. Other
scantools on the market range from simple hand-held meters that
display trouble codes, up to a large console computer-based
unit costing thousands of dollars.
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What
good does it do to measure OBD-II output?
OBD-II signals are most often sought
in response to a "Check Engine Light" appearing on the dashboard
or driveability problems experienced with the vehicle. The data
provided by OBD-II can often pinpoint the specific component
that has malfunctioned, saving substantial time and cost compared
to guess-and-replace repairs. Scanning OBD-II signals can also
provide valuable information on the condition of a used car
purchase.
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Tell me about that
"Check Engine Light".
The service industry calls the Check
Engine light on your dash an "MIL" or Malfunction Indicator
Light. It shows three different types of signals. Occasional
flashes show momentary malfunctions. It stays on if the problem
is of a more serious nature, affecting the emissions output
or safety of the vehicle. A constantly flashing MIL is a sign
of a major problem which can cause serious damage if the engine
is not stopped immediately. In all cases a "freeze frame" of
all sensor readings at the time is recorded in the central computer
of the vehicle.
Hard failure signals caused by serious
problems will cause the MIL to stay on any time the car is running
until the problem is repaired and the MIL reset. Intermittent
failures cause the MIL to light momentarily and they often go
out before the problem is located. The freeze frame of the car's
condition captured in the computer at the time of the malfunction
can be very valuable in diagnosing these intermittent problems.
However, in some cases if the car completes three driving cycles
without a re-occurrence of the problem, the freeze frame will
be erased.
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OBD-II
and your car's health
Because of their investment in the
equipment required, most repair shops charge a fee, some-times
substantial, to attach the scanning equipment and diagnose problems
using the OBD-II system signals. Home mechanics and small shop
technicians have been restricted from working with these signals
by the cost and technical complexity of the equipment. With
the introduction of more economical and user friendly scanning
devices, it is now practical for almost anyone to access OBD-II
signals and use them for their own testing and repairs.
Scanners vary greatly in their complexity.
The best connect easily and use software to quickly and automatically
call up the OBD-II information. They should have recording ability
so that data can be collected during a test drive without distracting
the technician driving the car. A system connecting to a laptop
or desk top computer provides expanded memory for data and the
ability to export data to a spreadsheet or graphing utility.
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Proprietary
Sensor Readings
Though not part of the EPA's OBD II standard, the diagnostic
read-outs used by dealership technicians are also read through
the OBD II connector. These service codes show you such things
as knock sensor operation, FI pulse width, ignition voltage,
individual cylinder misfires, transmission shift points and
ABS brake condition. There can be over 300 readings available,
depending on the vehicle manufacturer and model. Vehicles vary
in the readings they will support. Scanners vary widely in the
number of these signals that they can read. Some show
just the basic OBD or OBD II signals, others show the full range
of service codes.
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OBD-II
and performance tuning
While the vast number of drivers
want nothing more than dependable, economical transportation,
many of us are looking to OBD-II for extra performance. Earlier
on-board computer systems had chips that could be replaced to
adjust engine parameters for extra speed and power. While the
OBD-II systems are sealed and do not allow chip replacement,
they do provide a real time data acquisition system that is
useful to tuners.
Power loaders can actually reprogram
the performance parameters of the OBD-II system to accommodate
performance options. At the current time the number of models
they can service is limited, but the range is being extended.
Be sure the person doing your reprogramming keeps the car in
compliance with EPA emission standards. As aftermarket manufacturers
develop additional solutions, we will add their information
to our links.
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