At last, here's a positive indication what that is about, rather than just a 'contact support, it is serious' sort of documentation:
CTD Sensor Error Message CTD (ADC) Sensor Error is Detected
One person reporting this error (and that Fuji Xerox's remedies failed to help) reported abundant waste toner or loose toner or leaked toner powder in the bottom of the machine.
I advise checking for that. And doing a thorough cleaning-out of the machine, following these instructions scrupulously, also... esp. being careful to clean, but not damage, the CTD Sensor:
It is usual, with all laser printer problems, to Open, Inspect, Clean (carefully), Close Up, and Try Again.
Open: Unplug the machine for safety. Get access to the internal workings, esp. those of the problem area. Remove cartridge(s) if necessary.
Inspect: look for anything wrong or odd in the problem area. Spilled toner? bent or broken parts? stuck sensor switch? tabs or tape not removed from toner cartridge(s)?
Clean (carefully): Take a dry white or light colored high-quality lint-free rag cloth, and wipe firmly all possible plastic or especially metal surfaces that could have toner/paper dust/fluff/anything on them. Carefully, to avoid touching, spraying, moistening, abrading, or exposing to direct light for longer than 1 minute out of 15 or more, the shiny, usually blue-green (but sometimes red-purple) photosensitive 'drum' or roller, which is easily damaged.
Note: This is Xerox's recommendation with illustrations, as to cleaning the CTD sensors:
Close up: put everything back in, close covers, etc.
Try again: plug in, turn on.
- Let me know what you observe or find out. There may be more to do for the problem.