An illuminated Check Engine Light symbol or Service Engine Soon message indicates a problem with your vehicle's on board emissions control system(s). If the symbol or message illuminates, it will either blink or remain constant, depending on the problem. Either way, you should have your vehicle checked by one of our technicians as soon as possible. However, a blinking light indicates a problem that needs immediate attention. 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. 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 "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. The main purpose of this is to keep the engine running at top efficiency with the lowest possible emissions. In 1996, under federal OBD II regulations, carmakers were required to install a sophisticated system that essentially acts like a built-in state emissions testing station. The system 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 a loose or missing gas cap. When it finds a problem in the electronic-control system that it can't correct, the computer turns on a yellow warning indicator (Malfunction Indicator Light - or MIL) that's often labeled "Check Engine," or "Service Engine Soon". Sometimes the light may be nothing more than a picture of an engine, known as the International Check Engine Symbol, perhaps accompanied by the word "Check." In addition to turning on the light, the computer stores a "trouble code" in its memory that identifies the source, but not necessarily the cause, of the problem, such as a malfunctioning sensor or a misfiring engine. The stored trouble code and description can only be retrieved with a special scan tool. The code itself does not necessarily tell what part to replace; it only gives a general direction in which to look. Our technician must perform certain tests specific for each code to find the exact cause of the problem. There are many reasons for a Check Engine Light, and many causes for any one of the associated trouble codes.
In a late-model car, an illuminated MIL is almost a sure sign your car will fail a DEQ test. In Oregon, it's an automatic failure, even if the problem was nothing more than a loose gas cap. Lastly, 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 without the root problem being addressed.