To find out which ink cartridge is empty, check
EPSON Status Monitor 3 (for Windows)
or EPSON Status Monitor (for Macintosh)

You can also tell which cartridge is empty by checking the speed at which the error light flashes when the print head moves to the ink cartridge replacement position.

Replace the black ink cartridge if the error light flashes at the same speed as the power light.

Replace the color ink cartridge if the error light flashes at twice the speed of the power light.

Replace both the black and color ink cartridges if the error light remains on.