Canon printer won't print, yet no error

I have a new imageCLASS MF753cdw printer, working fine (still on original toner cartridges). Today my Windows print queue reported a printer error and would not print (and troubleshooter did nothing). I restarted Windows, no difference, not a windows issue. (I'm a 20 year IT person, so I think I've done the obvious) On the printer LCD screen was a warning to prepare toner cartridge CYM (all three report as 50% consumed). But no errors on screen! I tried shaking the toner cartridges as suggested on this Canon article: https://support.usa.canon.com/kb/s/article/ART153338 The LCD screen kept taki

Question by TSG on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.