This generation of Sharps have a horrible design for the drum / dv motors. I have replaced dozens of these motors over the past 3 years or so. The lack of drive, mostly occurs on black, prohibits the dv unit from spinning, the toner feed tubes get backed up and the material gets sucked out. I believe F2 codes only happen when the toner reading is below 73 or above 225 (or something like that). The first thing I always do with these codes is run 25-1 for 10 seconds. The result will tell you if you are over or under toned.
My 2 cents..