Am I the only one that thinks the dealer is just guessing like the rest of us? I hope he is a good guesser.
While you can make an educated guess unfortunately with modern electronic doodads more often than not the fix is found by replacing the suspect component with a known good one.
Many, many moons ago the wife had a giant mid-70's Buick with GM's HEI pointless ignition and one day it died about a quarter mile from the house. After pulling it home I found out the spark had gone away. Calling several car-savvy people I knew all told me to replace the ignition module. Not wanting to buy a component and it not be the problem I started calling GM dealerships to see if anyone had the equipment to test the module as mentioned in the shop manual. Despite Indy having a shitload of GM dealerships no one had this test equipment. One dealership mentioned that a tech that no longer worked there had bought the tester and as it turned out was now working at a tire shop not far from my home.
I called the shop, indeed the fellow was working there and incredibly had the tester in the trunk of his car. I raced over, let him test it (twice), he pronounced it to be good and charged me five bucks. The catch? He also said the only way to know for sure was to replace it with a known good unit. I stopped at a discount auto parts store on the way home, bought a lifetime guaranteed module, installed it and the car fired right up.
The reason I'm sharing this with you is that someone on this forum is going to experience a failure of a gizmo on their Grom and the dealer is going to start buying and plugging in components until they find the problem--and you may be charged for not only the parts but their labor in finding it as well.
Maybe a thread ought to be started for folks who suffer a failure of a component so the rest of us can know what to expect and whether or not we see a pattern of failures of these component(s). Once the bikes are out of warranty not many of us can afford the $75-125 an hour labor rate dealers charge and the knowledge of what commonly fails might help the rest of us keep our Groms running.