United States
                    Environmental Protection
                       Air and Radiation
September 2000
                    Office of Transportation and Air Quality
                   What To Do With the Check Engine Light
                    If you drive a 1996 or newer car or truck, you'll be glad to know that
                    your vehicle is equipped with an early warning system which could save
                    you time, money, fuel, hassles and even help protect the environment!

                    What does that light mean?
                    All '96 and newer cars and trucks have a powerful computer which
                    manages and monitors the vehicle's operation. This technology is called
                    "second generation On-Board Diagnostics (OBDII)." The computer
                    makes sure your engine runs at peak efficiency and will alert you of any
                    emission problems which need attention.
                    How do I know my car is working correctly?
                    You should see the "service engine soon" or "check engine" light flash
                    briefly when you turn your vehicle on. That tells you the system is doing
                    its job. After briefly flashing at startup, the light should normally stay
                    out while the vehicle is in operation.

                    What does it mean if the light turns on while I'm driving? If the light
                    comes on and stays on, your car may not be operating properly and
                    could  have a condition which wastes fuel, shortens engine life, or could
                    lead to expensive repairs if left unaddressed. It could also be polluting
                    the air. For example, OBD can identify everything from a loose or
                    missing gas cap (which contributes to smog) to a severe misfire (which
                    can lead to engine damage).
                   What should I do if the light comes on?
                   Don't panic! The car will not stop running or self-destruct. It's just
                   telling you to seek attention soon. If the light is blinking, a severe engine
                   problem like a misfire is occurring which should be addressed quickly.
                   You can still drive safely but should minimize driving. Try not to drive
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the vehicle at high speed or with excess
weight. Seek repair assistance quickly.
When you reach your destination make
sure the gas cap is not loose or missing.
(Don't refuel with the engine running, as
that may turn the light on.) Make an ap-
pointment with your repair technician for
diagnosis soon. Delaying assistance could
lead to more expensive repairs or damage if
left unattended for too long.
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Ask your repair shop if they are trained to
work on OBDII equipped vehicles. A
modern repair shop or dealership should
have an OBDII scan tool to diagnose the
cause of your vehicle's problem. The
technician will connect a small, hand-held
scanning device to your vehicle's computer
(usually through a connector under the
dashboard) and download special codes
which help to pinpoint the problem(s). The
technician then uses a manufacturer recom-
mended repair protocol to fix the vehicle
based on the registered code(s). After the
repair is complete, the technician will use
the scanning device to make sure the repair
was successful. OBDII actually helps
repair technicians do their job more quickly
and reliably (avoiding unnecessary repairs
and returns to the shop), saving you money
in the long run!
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If the problem that caused the light to come
on disappears within a few trips  perhaps
after the gas cap has been tightened or a
fouled spark plug has cleared  the OBDII
computer will turn the light off. This is not
an indication of a faulty OBDII system. In
fact, the system is doing its job to verify
that a problem existed that has been fixed
or gone away. Your car needs no special
attention unless the light comes on again.
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Today's vehicles are amazingly sophisti-
cated and highly efficient. OBDII helps to
make sure these new vehicles are running
in top shape. But you still need to make
sure that you maintain your vehicle accord-
ing to the manufacturer's recommended
schedule. Keep up that routine maintenance
and keep an eye out for your check engine
light; you'll be more likely to get extra
years of service out of your vehicle and
save money (both in fuel and repairs) while
helping to do your part to protect our
environment. As always, if you really want
to do what's best for air  quality, drive as
little as possible. Combine trips and car-
pool when possible.

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You can access documents on on-board
diagnostics electronically on the Office of
Transportation and Air Quality (OTAQ)
Web site at:

     http ://www. epa.gov/otaq/obd.htm

You can also contact the OTAQ library for
document information at:

     U.S. EPA
     OTAQ Library
     2000  Traverwood Drive
     Ann Arbor, MI 48105