Canon D340 "install cartridge" message

[partly retired]

Don't know what they did to copier but the message "install cartridge" won't go away. Tried multiple cartridges. I can see drum drive engages and does turn drum in toner cart. I don't know what determines toner cartridge is present. Interior right side black plastic piece, shaped around toner cart engage/drive, is broken at the top but spring finger that pushes down and holds toner cart in place, to engage with drive, is still there ( I know bad description). Any help is appreciated. Thanks

[partly retired]

I removed the drum flap, installed toner cartridge and copier worked. Don't know why. I know on some machines the drum flap actuates a sensor but not on this copier. But I still can't figure out why removing the flap allowed it to work.

[rapidocument]

Cartridge presence is checked by means of a HV current going through the charger roller and then tru the drum and finally drum ground, (and machine associated contacts) if for some reason (dust, dirt, bended contacts, missing contacts) this is not achieved, the machine sends an "install cartridge" message, I believe that by removing the drum cover you somehow cleaned (repositioned)? some contact(s) and machine entered to ready state.