The “check engine” light indicates an engine fault code has been logged. The engine may perform at less than optimal, from the computer’s point of view, but remain functional for years. That light will come on if a sensor, such as exhaust gas return valve, indicates a high reading. It may also indicate a fault from the mass air sensor, or that the fuel air mix is running rich. Generally speaking, orange lights on the dashboard indicate the vehicle is safe to continue driving, red lights indicate action needs to be taken immediately. If you happen to drive a Dodge Caravan (as my wife does) the check engine light indicates a fault but one that can be dealt with eventually. If the light blinks off and on then a serious engine fault exists which may damage the catalytic converter. If the engine is missing on one or more cylinders then unburned gasoline is passing through the exhaust and will burn up the catalyst. The check engine light indicates the complicated balance of fuel/air/spark is less than perfect. If something is really wrong other warning lights will start coming on. Then you actually need to do something.