What's That Light Mean?

So 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 people, you have little idea about what that light is trying to tell you or exactly how you should react.

We call it the most misunderstood indicator on your dash board. The "check engine" light can mean many different things, from a loose gas cap to a seriously misfiring engine.

Ignore this 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.

So, what is  the "check engine" light? This light is part of your car's on-board diagnostics (OBD) system. Since the 1980s, computers control and monitor vehicle performance, regulating such valuables 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 electronics-control system that it can't correct, the computer turns on a yellow warning light that is labeled "check engine", or "service engine soon."

This light could also be a picture of an engine, know as the Intentional 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 diagnostic computer, standard equipment in most auto repair shops.

Tips if Your Check Engine Light Comes On

Check your dashboard gauges and lights for indications of low oil pressure or overheating. These conditions mean you should pull over and shut of the engine as soon as you can. On most cars, a yellow "check engine" means investigate the problem giving you time to schedule an appointment to have your car diagnosed.

• Try tightening your gas cap. This often solves the problem. Keep in mind that it may take several trips before the light resets.
• Reduce speed and load. If the "check engine" light is blinking or you notice any serious performance problems, such as a loss of power, reduced your speed and try to reduce the load on the engine.
• In most cases, you're probably better of taking your vehicle to a professional instead of trying to diagnose the problem yourself. Make an appointment with a service center to have the codes read and the problem fixed.
• Don't go for a state emissions test. In a late model car an illuminated "check engine" light is a sure sign your car will fail the test. 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 vehicles computer will let the inspection station know that codes have been erased, and you'll just have to go back again.