United States
Environmental Protection
Agency
Office of Air and Radiation
6401
. April 1997
;EPA#420-F-97-004b
The Drive to
An Introduction
to Enhanced Vehicle
Emission Testing
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About the Emission Testing Law
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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" 1/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 manufacturer's 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 vehicle's fuel efficiency by an aver-
age of 6% to 13% by having the problem repaired.
This could mean a savings of $40 to $90 per vehicle
every year.
In addition to lowering fuel costs and increasing
your engine's efficiency, high-tech test-only emission
testing is the most effective, least expensive way to
identify polluting vehicles, which are the largest
single source of air pollution in the United States.
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"•• Emissions and the Environment
•*^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 theair
we breathe. It enters the bloodstream through die
lungs and forms a compound that inhibits the blood's
capacity to carry oxygen to the brain and tissues.
This poisonous gas affects the elderly, infants,
people with heart and respiratory disease, and
even healthy individuals when diey exercise.
Acute exposure to CO can cause brain damage.
Motor vehicles typically contribute 90% of the
carbon monoxide pollution in urban areas.
V 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
filtering out ultraviolet radiation from the sun. At
ground level, however, ozone can be damaging to
plants, animals, and human tissue. Ozone is also a
severe irritant that causes the choking, coughing, and
stinging eyes associated with smog. High ozone con-
centrations can present serious problems for children,
the elderly, and those with existing lung conditions.
In typical urban areas, as much as one-half or more
of these pollutants come from cars, 'trucks and buses.
How Do Emission Tests Work?
'**" Emission tests check the gases your exhaust system
releases and diagnose how well the entire system is
working. They compare your actual emissions to
the 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
the level of air pollution in your area.
Basic I/M is used in areas with only moderate air pol-
lution problems and consists of three types of tests:
^ An exhaust test measures emissions through a
hose hooked up to the tailpipe while your vehicle
idles.
> 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.
X A visual check of major emission control
components.
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
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in areas where pollution is more severe. The tests are
very effective because they simulate actual driving con-
ditions (including idling, acceleration, various speeds,
and load levels) allowing emissions to be calculated
more realistically. In addition, the sophistication of
this technology reduces or eliminates raise 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:
X An exhaust test accurately measures, under
real-world driving conditions, the amount of
pollutants 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.
X A purge test determines whether die 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
(as described under the basic I/M test).
>• A visual check of major emission control
components.
The Future of Emission Testing
-Only by testing can we be sure that a vehicles
emission control system is working properly.
Todays 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 the technician isolate die
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 the
systems in a vehicle. OBD checks, if found to be
effective, may replace odier kinds of tests in die
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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