Hi,Clean Patch Sensor first but could be faulty sensor/drum/devs etc.
Pasted from another reply
i have one of these damn c3100 that has eatin 2 drums when it throws the e0020-0081 code. the drum has a perfectly straight line the exact width of the mag roller. the customer has not used color much and appears to be having issues related to this. is it possible the toner and developer built up too thick and has rubbed the drum? that appears to be what is happening. man do i hate c3100s! please help. thanx
When an E020-0081 error code is displayed on the control panel (when the value of [P-SENS-P] has
detected as being less than 255) while the background of the image on the drum is being checked upon
power-up or recovery from sleep mode, the machine stops operation with the bias voltage applied to the
charging roller. This leaves the charging roller mark on the drum surface.
When the imageRUNNER is activated with 50°C or lower fixing roller temperature
and the potential of the photosensitive drum is measured at initial rotation, an E020-
0081 occurs. The line caused by the charging roller remains on the surface of photosensitive
drum. A modification is made, so that the charge to the charging roller is
disabled at the emergency stop. upgrade the DCON > DCon 45.01
Make sure u have Firmware 45.01 or later+