Dell 2350d/dn Mono Laser Printer - Manual (Page 141)

You are using paper that does not meet the printer specifications.
The toner cartridge is low on toner.
The toner cartridge is defective.
Try the following:
Select a different Toner Darkness 1 setting before sending the job to print.
Load paper from a new package.
Avoid textured paper with rough finishes.
Ensure that the paper you load in the trays is not damp.
Replace the toner cartridge.
Print is too dark, or the background is gray.
The Toner Darkness 1 setting is too dark.
The toner cartridge is worn or defective.
Try the following:
Select a different Toner Darkness 1 setting.
Replace the toner cartridge.
White lines appear on the page.