I've had the bike for about 700 miles. It has about 500 miles now. ABS light comes on randomly and stays on for a while. Sometimes it goes away on its own. What would be some causes of this happening? I don't ride it hard but don't know how the previous owner rode it.
You could do a visual of the components to see if any obvious faults are present.
The phonic wheel rings have a specified min-max runout difference of 0.40MM checked at 90 degree rotations. The book says to replace it if it does not meet specification. I suspect most people would just try to straighten it. The sensor air gap is 1.3 to 1.9MM and is adjusted with shims.
If nothing is noted with a visual, best bet is to take it to a dealer. They have a test set (ABS 8M) which hooks up to the connector under the seat and the battery. It will do a diagnostics test as well as read stored fault codes.
The "goes away on its own" would concern me because once illuminated with a fault, it should stay on.