Check the smc for pcdu lifetime. Printout the test page in printer sp and have look to the yellow patterns. By the way, you should disassemble waste toner box, all pcdus, fusing and itb unit, to clean the id sensors. I think you have to swap the pcdu yellow!!!

When you disassemble the laser unit so pull out the toner bottle and suck off gently the toner housing from toner soilings.