What would cause my 2007 mercedes s550 check engine light to come on?

If You are driving Your 2007 Mercedes S550 and a check engine light comes on at the dash the first thing You should do is try to get off the road to a safe place as soon as possible. Once You have stopped You should use an OBD II scan tool to read the code that was thrown to the ECU that caused the light to turn on. There are many different reasons why Your light can turn on. It could be something as simple as a loose gas cap, all the way up to as complexAs an ECU failure. Without a scan tool there is no good way of knowing what it is.