How do I know when an ink cartridge needs to be replaced?

• When the printer's Error light flashes, an ink cartridge is low on ink. This is a good time to make sure you have a new cartridge handy. When the Error light stays on, a cartridge is empty and you need to replace it.
  
  The red error light also comes on if your paper runs out or is jammed, so make sure to check your paper before replacing a cartridge.
  
  Check the LCD display codes on the printer to see which cartridge is low or empty.
  
  ILc = Color Low
  
  ILb = Black Low
  
  IEc = Color Empty
  
  IEb = Black Empty
  
  If you're printing from your computer, you'll see a message telling you which cartridge is low or empty. Click the 'How to' button to see instructions for replacing the cartridge.
  
  When a cartridge is more than six months old, you may need to replace it if printouts don't look their best.
  
  If the quality doesn't improve after cleaning and aligning the print head, you can replace the cartridge even if the red error light is off.