I have 2011 duramax. A couple of weeks ago I had my def poor quality message come on. I followed the owners manual guidelines added 2.5 gallons fresh, drove down the highway 20 miles and the light cleared. I have not any problems for over 500 miles. This morning driving to work the message came back. The mil check engine is off and no codes found. Ambient temp this morning was 30. Does any one have ideas what is going on? Is there way to turn this light off ?