Canon MG6400 SERIES Online Manual page 171

(2) Confirm the message, then press the OK button.
The screen will return to the Maintenance screen.
Note
Press the HOME button to exit Setup and display the HOME screen.
For (B) (lines are missing or horizontal white streaks are present) in the pattern
(C) or pattern (D), or in both patterns:
(1) The cleaning is required. Select Also B, then press the OK button.
The cleaning confirmation screen will appear.
(2) Select Yes, then press the OK button.
The machine starts cleaning the print head.
Cleaning the Print Head
Note
The total number of sheets printed so far is shown in increments of 50 sheets on the
printout of the nozzle check pattern.
171