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.
The "check engine" light is part of your car's onboard diagnostics (OBD) system. Since the 1980s, computers control and monitor vehicle performance, regulating such variables as engine speed (RPM), fuel mixture, and ignition timing. In some vehicles, the computer also tells the automatic transmission when to shift.
When the computer 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," or "service engine soon.” This light could also be 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.
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 service technician. Your “check engine” 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 not corrected. 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.
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 most cars, a yellow "check engine" means investigate the problem giving you time to schedule an appointment to have your vehicle diagnosed.