Your Gas Cap is Loose. When you start your vehicle, it runs an evaporative test on the fuel system.If there is a leak detected, it will turn on your ses/check engine light. Thefirst thing you want to check is that your gas cap is on tight. If that was theproblem, your light should turn off after a few engine cycles.(every time you start your car is an engine cycle) Bad Spark Plugs When your spark plugs wear out, your vehicle will start to missfire. This willcause your ses/check engine light to come on. Replace your spark plugs andwires, and have an auto part store clear the ses light. Fuel Injectors Clogged. When injectors get clogged they may turn your ses light on. You should alwaysclean your injectors every 25k miles. You may be able to tell if you need themcleaned if the car lacks accelleration, or the gas pedal sticks when pressed. Read more about Check engine light. Most repair facilities can take care of that for you. O2 Sensor Failure. Your O2 sensor tells your car how much fuel to mix with the air. If this isfaulty you may notice very poor gas mileage. Have your O2 sensor replaced. EGR Valve Stuck/Dirty The EGR Valve recirculates exhaust emmissions back to your intake systemto be burned off. This reduces the amount of pollution given off by your vehicle.If this gets dirty/stuck it will set your ses/check engine light on. Try a full fuelservice on your vehicle to get dirt/carbon buildup off the EGR valve. If thisdoesnt work, you may need to replace the EGR valve. NOTE: If the above repairs do not solve your ses/check engine light problems, your vehiclewill have to be diagnosed by a mechanic. I recommend taking it to your manufacturersdealer, as they are more familiar with your car and can save you from replacingunnecessary parts. For more info visit Check engine light.