WHAT TO DO IF YOU GET DEF IN YOUR FUEL
If you suspect you have DEF in your diesel’s fuel system, do not drive the vehicle and do not attempt to start the engine. Don’t even turn the key on, as this will energize the fuel system and could pump Def-contaminated fuel into the rest of the fuel system. If the error is caught before the key is turned, the fix may be as simple as dropping the fuel tank and flushing it out.
Have the vehicle towed or flat-bedded to a repair facility, and if you need to unlock the steering column, be sure to disconnect the batteries before turning the key in the ignition. Make sure to get your vehicle repaired right away, as DEF is corrosive and letting it sit in the fuel system can cause further damage.