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发帖数: 1828 | 1 You're driving along in your car or truck and suddenly a yellow light
illuminates on your dash telling you to check or service your engine. If you
're like most car owners, you have little idea about what that light is
trying to tell you or exactly how you should react.
Call it the most misunderstood indicator on your dashboard, the "check
engine" light can mean many different things, from a loose gas cap to a
seriously misfiring engine.
"It doesn't mean you have to pull the car over to the side of the road and
call a tow truck. It does mean you should get the car checked out as soon as
possible," says Dave Cappert of the National Institute for Automotive
Service Excellence, a Virginia-based organization that tests and certifies
auto technicians.
Ignore the warning, and you could end up damaging expensive components. It
also can be a sign that your car is getting poor fuel economy and emitting
higher levels of pollutants.
What the Light Means
The "check engine" light is part of your car's so-called onboard diagnostics
(OBD) system. Since the 1980s, computers increasingly have controlled and
monitored vehicle performance, regulating such variables as engine speed (
RPM), fuel mixture, and ignition timing. In some cars, the computer also
tells the automatic transmission when to shift.
When it finds a problem in the electronic-control system that it can't
correct, the computer turns on a yellow warning indicator that's labeled "
check engine," "service engine soon" or "check powertrain." Or the light may
be nothing more than a picture of an engine, known as the International
Check Engine Symbol, perhaps with the word "Check." In addition to turning
on the light, the computer stores a "trouble code" in its memory that
identifies the source of the problem, such as a malfunctioning sensor or a
misfiring engine. The code can be read with an electronic scan tool or a
diagnostic computer, standard equipment in auto repair shops. There are also
a number of relatively inexpensive code readers that are designed for do-it
-yourselfers.
Manufacturers originally used the OBD system to help technicians pinpoint
and troubleshoot malfunctions. But the systems now are required under
federal laws governing automotive emissions. Although larger trucks have
been exempt from the requirement, that quickly is changing.
"The 'check engine' light is reserved only for powertrain problems that
could have an impact on the emissions systems," says John Van Gilder,
General Motors' lead OBD development engineer.
Exactly what the OBD system looks for depends on the make, model and year.
The original systems varied widely in their capabilities. Some did little
more than check whether the various electronic sensors and actuators were
hooked up and working.
That changed by 1996, when, under OBD II regulations, carmakers were
required to install a much more sophisticated system that essentially acts
like a built-in state emissions testing station. The computer monitors and
adjusts dozens of components and processes. For example, it continually
samples exhaust emissions as they come out of the engine and again when they
leave the catalytic converter, a device that removes carbon monoxide and
hydrocarbon pollutants from the exhaust. The system also monitors your car's
fuel system to ensure that gasoline vapors are not escaping into the
atmosphere through a leak or even a loose or missing gas cap. In most cases,
if a problem occurs, the computer will wait to see if it corrects itself
before turning on the light. Modern OBD II systems are so thorough that
state testing centers increasingly are checking for any stored trouble codes
and foregoing the traditional tailpipe emissions test.
Some states are considering an advanced OBD system that would allow them to
do away with emissions testing. If the "check engine" light comes on, the
system automatically would send a remote signal to state officials, who
would contact motorists who don't have the problem corrected within a
reasonable amount of time. Privacy advocates are criticizing the idea as
being too intrusive. Depending on the system, officials might be able to
trace where the vehicle had been. Proponents say the system would free
motorists from the time and expense of having to undergo annual or biennial
emission testing, and it would help ensure that emission-related problems
are detected and fixed more quickly.
Remote diagnostics already can be found on GM vehicles equipped with the
OnStar communications system. When the "check engine" light goes on, GM car
owners can notify an OnStar representative, who can read the trouble code
and provide advice.
What to do
If your "check engine" light illuminates don't react like one Connecticut
motorist, who simply poured an extra quart of engine oil into her 2002
Toyota Corolla. Although extreme situations, such as low oil pressure or an
overheating engine, might trigger a "check engine" light, your dashboard has
other lights and gauges to warn you about those problems and probably a lot
sooner. The best advice is to read your owner's manual beforehand and learn
the purpose of the "check engine" light and every other gauge and warning
indicator on your dashboard. Periodically, you also should test the "check
engine" light and other dashboard warning lights. Usually, you can do this
by turning the key to the key-on/engine-off position. Consult the owner's
manual for more information. Replace any bulbs that aren't working.
If the "check engine" light illuminates, it will either blink or remain
constant, depending on the problem. Either way, you should have the vehicle
checked by a mechanic, although a blinking light or, on some cars, a red
light instead of a yellow/orange light indicates a problem that needs
immediate attention. In late-model cars, a blinking light usually indicates
an engine misfire so severe that unburned fuel is being dumped into the
exhaust system, where it can quickly damage the catalytic converter,
requiring an expensive repair. If that happens, you should reduce power and
have the car or truck looked at as soon as possible. If the light is steady,
the problem is not an emergency, but you should schedule an appointment as
soon as possible. Today's automotive computers often try to compensate when
there's a problem; so you may not notice deterioration in performance, even
though your fuel mileage is suffering and your vehicle is emitting
unacceptable levels of hydrocarbons and other pollutants.
"The customer is really, in the long run, potentially hurting their pocket
book by leaving that light on and ignoring it," says Jim Collins, a national
training team leader for Ford Motor Company. In some extreme cases, the car
's computer may reduce power for you, as it tries to limit the risk of
damage.
If the check-engine light comes on, here are some tips on what you should do:
* Look for a serious problem that requires immediate attention. Check
your dashboard gauges and lights for indications of low oil pressure or
overheating. These conditions mean you should pull over and shut off the
engine as soon as you can find a safe place to do so. On some cars, a yellow
"check engine" means investigate the problem, while a red "check engine"
means stop right now.
* Try tightening your gas cap. This often solves the problem. Keep in
mind that it may take several trips before the light resets. Some vehicles
have a separate indicator that warns of a loose gas cap before the condition
sets off the "check engine" light.
* Reduce speed and load. If the "check engine" light is blinking or you
notice any serious performance problems, such as a loss of power, reduce
your speed and try to reduce the load on the engine. For example, it would
be a good idea to stop towing a trailer. Have the car checked as soon as
possible to prevent expensive damage.
* Contact OnStar, if available. If you have a 1997 or later General
Motors vehicle equipped with OnStar and an active OnStar subscription,
contact an advisor who can read the trouble code remotely and advise you
about what to do.
* Have the code read and the problem fixed. If you want to diagnose the
malfunction yourself, you can buy a scan tool at most auto parts stores.
Prices range from about $40 to several hundred, depending on the model and
the features. The tools come with instructions on how to hook them up and
decipher the codes. But unless you have a good knowledge of automotive
diagnostics, you're probably better off taking the vehicle to a professional
. Some automotive parts stores will read and interpret the code for you
without charge. Unless there is an easy fix, they may simply refer you to a
mechanic.
* Don't go for a state emissions test. In a late-model car, an
illuminated "check engine" light probably is a sure sign your car will fail
the test. In some states, it's an automatic failure, even if the problem was
nothing more than a loose gas cap. By the way, don't bother trying to fool
the inspection station by disconnecting the battery or using any other
method to erase the trouble code and turn off the "check engine" light. Your
vehicle's computer will let the inspection station know that its codes have
been erased, and you'll just have to go back again. |
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