Mine has a yellow light, don't lose sleep. In the cummins engine it is simply completing a "regen." I'm sure there are a number of posts coming that will give you an idea of what happens during this cycle. All I see is a bit of white smoke during this process and then the light goes off and I don't see it again for a couple thousand miles. Depending on the type of driving we're doing. Interstate vs stop and go through large cities or secondary highways, the time between regen is different.
09 Magna Donatello
"The Flying Salesman"®