I have gotten this message twice this week...both times I was going downhill braking to a stop and got the beep and message...of course the master cylinder is full...just a glitch?
Mine did that too as my brakes wore down probably around 55,000 miles I think. Replaced front pads around 60,000 back pads around 70,000 and needed new rear rotors which we're wore down from what I guess are very hard pads. I think all the original brake squealing was the rotor being wore down...
25k on mine now and reservoir is full so I dont know... the sensor may be in the back since I was going downhill and braking it may have just tripped it...