DEF indicator lamp

Did you top off the tank? I would make sure there is enough fluid first then go from there. How does the truck run? losing power?

I have a prostar with issues like that. I believe mine is an electrical fault.

 

I have a 2012 Cascadia with DD13 and my truck does the same thing sometimes when I shut my driver side door. Indication goes out for 15 to 20 seconds on the DEF tank level indicator. So it is no coincidence and you are not going crazy. I wish I could add more. I do not have a solution. I have bigger fish to fry at this point for after treatment codes on another thread.

 

My truck is in the shop for DEF issues right now. I wanted to run something by you that maybe you can check. My truck is at the dealer so I can not check it right now. When you close the door....the inside dome lights above your head stay on for about 15-20 seconds. Look at the timing of the lights above your head and time it with how long your DEF level indicator goes out(or gets very dim) and how long for it to come back when the light above your head goes out. When the light above your head goes out does the DEF level indicator brighten back up or turn back on? If you can check it before me then please report your finding. Maybe the voltage for the DEF level indicator is also tied to the Voltage for the lights in the cab and the associated timer??? Worth a shot to time and look at. May be that simple. Please Advise.
D Rock