I would suggest buying a locking green fuel cap. That way you are aware that you unlocked the fuel but have DEF in your hands. The Stant part number is 10510D. You can get one off eBay for $14 or less shipped to you.
I also suggest never removing both caps at the same time. I always pull away from the pump before I put DEF in the tank and only fill the fuel tank as the pump.
I also suggest never removing both caps at the same time. I always pull away from the pump before I put DEF in the tank and only fill the fuel tank as the pump.