Canon S400 Reference Manual page 184

Check 1
Is the ink of BJ Cartridge in good condition?
The print head nozzles may be clogged, one or more of the ink tanks may
be low, or the BJ Cartridge may be worn. Visually check the level of the ink
in the ink tanks. If the tanks are empty, replace them. Next, print a nozzle
check pattern to check the status of the print head and clean the print head.
If the problem is not solved, replace ink tanks or BJ Cartridge.
If you can print a nozzle check pattern normally, check that the printer is
connected to the computer securely. If the connection is loose, printing
starts but nothing may be printed.
Make sure there is no problem with the original file.
Printing a Nozzle Check Pattern
Cleaning the Print Head
Replacing Ink Tanks
Replacing the BJ Cartridge
Troubleshooting - Printer Does Not Start or Stops in Mid-job
Printing starts but nothing printing
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