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
