This is an old thread, but I'm giving it a bump since I'm experiencing the same issue. Cycling the ignition does allow the grip heaters to start working again. Motoscan reports error codes A338 (right grip) and A33A (left grip), both with low voltage. Battery is only a couple of years old and tests fine.Pay attention to when you start the bike. I've had the same issue on my '13. Some mornings, the grips just wouldn't turn on. I'd have to turn the ignition off completely, let it reset, then fire it back up. There seems to be a problem with the CANBUS. If the grips are on when starting (or you turn them on before diagnostic check), the CANBUS seems to think there's a short. The solution is to turn the ignition to on, let it cycle for 30 seconds, then fire up the engine. Once the engine is running, then turn the grip heaters on. Sounds wonky, but didn't have any issues after but I only got to check it out for a short time before putting the bike in storage for overseas move. The dealership tested it out under various conditions to figure that one out. They didn't really have a solution other than that. There were no failures with any of the tests they ran.
I saw some posts on other threads suggesting checking the grip connections. I'm curious to know whether there are any other ideas out there.