1. Press MENU # 1 9 3 4 in sequence rapidly. The LCD panel should now display TECH.
2. Press MENU, and then press ENTER. The LCD panel will display Tech Mode.
3. Press the left arrow (<) button once. The operator panel will display NEW CARTRIDGE.
4. Press ENTER. The operator panel will display [YES].
5. Press ENTER. The toner warning message should be gone.
6. To exit TECH MODE, press MENU # 1 9 3 4 in rapid succession, as if you were dialing a phone number. The operator panel should no longer display TECH.
If problem persists, there may actually be a problem with either the toner cartridge or the SCX-4216F.
Works for SCX-4521F