Dunno what year your bike is, but As a systems admin, I'd say Treat it like a computer ...... Disconnect the sensor, disconnect the battery, then connect the battery back and start the bike.
Shut it off, disconnect battery, reconnect abs sensor, reconnect battery, then start the bike.
Ecu should detect the change between starts with the sensor disconnected on start, and then connected on restart.
That's worked for me in the past. You may have already tried that, if so my apologies, just something I had success with previously.
Very possible the sensor could be either dirty or bad, and it's a simple fix by just replacing the sensor instead of taking to the dealer and incurring that cost