I really don't know, my integral brake system worked flawlessly the entire time I had the bike.
The system should self-diagnose in a few seconds after turning on the key. You aren't holding the bike on a hill or anything while the bike is trying to self check are you?
The inside reservoir is for the front wheel circuit, don't know if that would effect the modulator operation, but it sure wouldn't do the pump any good. Plus the PO should have gotten a flashing warning light on the dash for low fluid in the reservoir.
Did you poke thru the "search" function? I'm sure there is a ton of information in there.
'04 K1200RS Capri Blue(totaled)
2008 Triumph Sprint ST