&EPA
United States
Environmental Protection
Agency-
Office of Air and Radiation
6401
April 1997
;EPA #420-F-97-004a
The Drive to
An Introduction
to Enhanced Vehicle
Emission Testing
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About the Emission Testing Law
In 1990, Congress amended the Clean Air
Act to require states to Implement vehicle
inspection and maintenance (I/M) pro-
grams. Highly populated areas that fail to
meet air quality standards must implement
either a "basic" or "enhanced" I/M pro-
gram, depending on the level of pollution.
The Act also requires additional controls
on stationary sources (i.e., power plants)
of air pollution, so everyone contributes to
solving this important national problem.
uying a car or truck is one of the biggest
investments you make. To protect that
investment, you must keep your vehicle in
good working order. An important way to do that
is to have your vehicle's exhaust emissions tested.
Besides reducing air pollution, emission testing can
help improve fuel economy and extend the life of
your vehicle.
Emissions and Your Vehicle
- High emission levels do more than pollute the air.
They are symptoms of poor engine performance,
which can cause decreased fuel efficiency and may
signal possible engine troubles down the road.
You can extend the life of your vehicle by following
the manufacturers maintenance recommendations.
Regular maintenance generally can help prevent
many emission problems from developing.
If emission problems do occur, studies show that you
can improve your vehicles fuel efficiency by an aver-
age of 6% to 13% by having die'problem repaired.
This could mean a savings of $40 to $90 per vehicle
every year.
In addition to lowering fuel costs and increasing
your engines efficiency, high-tech test-only emission
testing is the most effective, least expensive way to
identify polluting vehicles, which are die largest
single source of air pollution in the United States.
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Emissions and the Environment
" How Do Emission Tests "Work?
*- By identifying vehicles that pollute, emission testing
helps reduce risks to our health and the environment.
It specifically works to reduce emissions of two major
pollutants — carbon monoxide and ozone.
> Carbon monoxide (CO) is the deadliest com-
ponent of air pollution. It is a colorless, odorless gas
that results from incomplete combustion of fuel.
CO goes direcdy from a vehicles tailpipe into the air
we breathe. It enters the bloodstream through the
lungs and forms a compound that inhibits the bloods
capacity to carry oxygen to die brain and tissues.
This poisonous gas affects the elderly, infants,
people with heart and respiratory disease, and
even healthy individuals when they exercise.
Acute exposure to CO can cause brain damage.
Motor vehicles typically contribute 90% of the
carbon monoxide pollution in urban areas.
>" Another toxic component of air pollution is
ozone, formed when hydrocarbons (HCs) and
oxides of nitrogen (NOx) combine with sunlight.
Both HCs and NOx are emitted from vehicles.
In die upper atmosphere, ozone benefits life by filter-
ing out ultraviolet radiation from die sun. At ground
level, however, ozone can be damaging to plants, ani-
mals, and human tissue. Ozone is also a severe irri-
tant that causes the choking, coughing, and stinging
eyes associated with smog. High ozone concentra-
tions can present serious problems for children, the
elderly, and diose with existing lung conditions.
In typical urban areas, as much as one-half or
more of these pollutants come from cars, trucks
and buses.
"**" Emission tests check the gases your exhaust system
releases and diagnose how well the entire system- is
working. They compare your actual emissions to
die allowable standards for your vehicle model year
and type.
There are two types of inspection and maintenance
(I/M) testing programs — basic and enhanced.
Which test is required for your vehicle depends on
die level of air pollution in your area. Since most
motorists are familiar with basic I/M programs
begun in the 1980s, this brochure focuses on
enhanced I/M.
Enhanced I/M refers to performance-based
emission control initiatives selected by each state to
meet enhanced performance standards in reducing
air pollution locally.
There are several advanced technologies which can be
used to evaluate overall engine performance. These
high-tech, mass-based transient tests are currendy
used in areas where pollution is more severe. The tests
are very effective because they simulate actual driving
conditions (including idling, acceleration, various
speeds, and load levels) allowing emissions to be calcu-
lated more realistically. In addition, the sophistication
of this technology reduces or eliminates false passes
and false failures common in I/M testing.
A trained inspector, experienced in testing proce-
dures and proper handling of vehicles, drives the
vehicle onto a dynamometer (a vehicle treadmill)
and performs some or all of the following tests:
>• An exhaust test accurately measures, under
real-world driving conditions, the amount of pol-
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lutants coming through a vehicles tailpipe and
compares that amount to the allowable standards.
In general, tests take anywhere from 30 seconds to
four minutes, or about two minutes.
>• A purge test determines whether the gasoline
vapors are properly captured from the fuel tank
and charcoal canister and routed to the engine
where they are burned as fuel. This is essential for
pollution control and good fuel economy. This
test is performed during die exhaust test.
>• A pressure test checks the vehicles evaporative
emission control system for a proper seal.
X An on-board diagnostic (OBD) test.
Engine and emission control systems on todays
vehicles are controlled by on-board computers.
OBD computers monitor these systems and store
codes when a problem is found so inspection or
repair technicians can access these codes. The
OBD test checks a log for any emission control
problems recorded by the computer.
>-A visual check of major emission control
components.
In addition to IM240, there are other tests, inspec-
tions, and measures that states may select in develop-
ing their programs to fit their local needs.
By identifying vehicles that pollute,
emission testing helps reduce risks to our
health and the environment. It specifically
works to reduce emissions of two major
pollutants — carbon monoxide and ozone.
The Future of Emission Testing
- Only by testing can we be sure that a vehicle's
emission control system is working properly.
Today's tests are geared toward identifying emission
control issues and having them repaired. Emission
tests and other visual inspections rely on sophisticat-
ed computer technology both at the testing site to
recognize if and how the car contributes to the
pollution problem and at the repair facility where
diagnostic equipment helps die technician isolate
the cause so that it can be eliminated.
New technology, however, promises to make testing
even easier. For instance, all new cars and trucks are
equipped with OBD computers that monitor all die
systems in a vehicle. OBD checks, if found to be
effective, may replace other kinds of tests in the future.
Advanced technology in modern vehicles can gready
improve the quality of our air, but only if the engine
is functioning properly. As vehicle owners take
personal responsibility to maintain their vehicles and
verify their engine performance through emission
testing, America's #1 source of air pollution will be
put in check.
A well-maintained car will last longer, cost less to
operate, and be part of the solution to healthier,
cleaner air.
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