Def fuel light and check engine light on 2011 Kenworth

Probaly sensor,

 

That's telling the computer DEF tank is empty.

 

I had Freightliner same lights it was because low NOx conversion. First time they had to clean DEF system and that fixed it. Second time they claimed it was sensors. The last time the emissions box was bad because the DOC filter we're bad. On Freightliners they have the one box system and it was a crazy price to replace the emissions box. I think Cummins has separate DOC filters that can be replaced if cleaning the DEF system or replacing sensors don't work.

 

Ever find out what was wrong?

 

This happened to me once, but it would occur at random and eventually got worse. After replacing the Box Sensor and a def hose, the techs finally listened to me. I originally thought it was the fuel sender and the equivalent for the def tank, since both were affected. It turns out, there was a small short in one of the electrical wires causing the problem. So, after $2000, it was resolved with a $90 fix.... go figure. I Hope you found the problem.