Yellow check engine light
 

The Check engine light has come on in my 15 S550. This happend about a month ago and I call the dealership and that it’s likly a loose gas cap if the car is running normally. It went out in a few days and now it’s back on. The gas cap was never loose when I checked.
I am curious if anyone else has experienced this and if do what was the cause.

It's possible there is a faulty gasket on the gas cap. But, there are several other reasons a Check Engine light comes on. They all have to do with emissions control systems, such as cats. The only way to know for sure is to get the fault codes read.