My LG TROMM washer began to throw a 'dE' door error code and fail to start a wash load. I could usually get it to start by putting my pinkie in the door latch a few times to 'exercise' the switch. I also removed the door latch following the excellent instructions from appliancepartspros.com and cleaned the electrical contact that verify's the door is closed and locked with alcohol and cloth but that only helped for a couple of days.
I didn't try fine grit sandpaper but that might remove the oxidation on the electrical contact surfaces and fix the latch so that may be worth a try. The latch is held together by 3 plastic clips. Unclip them and it pulls apart easily. The electrical contact is on the end of a one inch long bar which closes when the washer door is closed and latched.
I broke down and ordered the replacement door latch from appliancepartspros.com and that solved the problem. To get the spring loaded boot clamp off and back on I used two hooked 'dental tools' with handles to pull the clamp's spring apart.