the 3361-6 code was for Dosing unit current above normal. 3361-5 is for current below normal. Something has changed. With an ohm meter can you test each of the wires that go to the DEF injector from the injector to the ECU that controls the injector? Measure the resistance of the injector at the injector and at the ECU. Are they very close to the same. I'm going to hazard a guess that the injector resistance should be between 10 and 50 ohms