Engine warning. Meaning something is over pressurized typically, it is sometimes accompanied by what almost looks like a Regen light but has an ! Instead of a temperature sign.
According to my owners manual (2012 4300 with the DT) Illuminates Yellow. Used in conjunction with other Warning Indicators or General Text and Warning Messages to indicate an Alert condition to the operator. Check the message center in your dash to see what it's trying to tell you.