Frequently Asked Questions The ‘Check Engine’ light comes on and stays on while my vehicle is running. What does that mean? Do I need a ‘tune-up?’ Is my ignition, fuel injection or emission control system malfunctioning? Servicing the engine management systems on today's computer-controlled vehicles is more than just a tune-up performed at regular intervals. That's why the ‘Check Engine’ light alerts you when there is a problem in your vehicle. When it lights, it means that your vehicle's on-board computer (known as the Electronic Control Module or ECM) has detected a problem in one of the many systems it monitors and controls. The problem may be minor, but it could be serious. What if the ‘Check Engine’ light comes on but my car is still running okay? Not every problem with your vehicle results in noticeably poor vehicle operation. When the ‘Check Engine’ light comes on, it means that some system in your vehicle, perhaps ignition, fuel injection or emission control, is not operating at peak performance…even if your vehicle appears to you to be running normally. What do the sensors and engine components in my car do? Your car’s on-board computer processes information it receives from the many different sensors around your car, then sends commands to other components throughout the vehicle. These sensors provide information to your vehicle about how the fuel delivery, spark timing, emission controls and other systems perform. For more information about what these components do, visit Just the Facts. Visit our Resource Library for available downloads