Emissions check engine light on 2013 Chevy 3500 Duramax?

I'll know the code tomorrow when I have it scanned. I was hoping someone here had already gone through something similar. I'm guessing bad diesel or air filter. DEF was added about 400 miles prior so I know that isn't the problem. The only recent thing done was a trucker fuel stop then about 100 miles later was the emissions engine light. Runs fine though.
Thanks to all who have replied so far. Any ideas?