Bruce,
I haven't done this but I think there is a way for you to flash the ABS codes. I scanned my ABS system book once and saw there is a way to read the code.
FWIW mine will stay on if it has been damp or raining just before I drive. The next time I turn the bus off after driving a while and then restart the bus it will go out. I have never bothered to check why it is doing that because when I get to a place where I can mess with it, it is usually not lit.