If you are not a Certified Gilbarco service provider, forget it. You need a lap top and a program to communicate, downloaded from Gilbarco using your Tech #.
You sound like a brand new tech. The first thing you need to do is go and look at the problem first hand instead of comming up with what if's before even viewing the actual problem. Could be as simple as the nozzle boot switch not working, or a bad grade switch. If I had a crystal ball I wouldn't have to go out on any service calls and would be a millionair.