Product review (5 stars): If door switch isn't broke, could be this.
Dishwasher Model GDT720SSFSS - had for 18 months.
Went to run it one day and it wouldn't start. After running the diagnostics, it appeared that it wasn't detecting that the door was shut. I tried replacing the door switch, but no difference. I ordered this as it is where the door switch plugs into. Took about 1 hour to replace (dishwasher was already pulled out and I had previously inspected the control board.) Part fit perfectly and worked immediately.