Link: http://www.computercare.cc/osc/catalog/laserjet-9000-series-c-74_146.html
Among the most common problems that you'll see in the HP LaserJet 9000 is the false 13.20 error. It will come up during or immediately after the power-up sequence, before you even try to print anything, and you won't find paper anywhere in the paper path. As in any printer, this can be caused by a stuck sensor flag, but in the 9000, there are some other potential causes: a defective fuser or DC Controller board, or bad high voltage connections.