Printing is faint in the vertical direction

Cause
Solution
Reference

The LED head is dirty.

Wipe the LED head with soft tissue paper.

Cleaning the LED head
The toner is low."Toner Low." or "Toner Is Empty. Replace With A New Toner Cartridge." is displayed, replace the toner cartridge.
Replacing the black(K) toner cartridge and the waste toner box
Replacing the toner cartridge (C/M/Y)
The paper is not supported.Use recommended paper.
Applicable paper