MaintenanceWorkCentre 6015 Color Multifunction Printer 155User Guide10. Align the black toner cartridge with the rear toner slot. Press firmly near the center of the cartridgeuntil it clicks into place.11. Replace the remaining three toner cartridges in the same manner.12. Close the side door.Cleaning the Color Toner Density SensorsNote: Clean the color toner density (CTD) sensors when an alert for the CTD sensors appears on thecontrol panel or in PrintingScout Printer Status window.1. Turn off the printer.2. Push down the rear cover release lever and pull open the cover.