My ED is still factory tuned, Yep I only use the Urea in winter or just before winter.. We have used urea in another business I'm associated with for decades very familiar with its properties and use, I'm at about 10% Urea in summer and 30-40% winter months.. I stop pulling My DEF Injectors on all My trucks. I pull My 2013 Many times up to 2015, it look New every Time , None of My DEF trucks have ever needed repairs or CEL.