Canon iPF670 User Manual page 548

When to Replace Ink Tanks
Before print jobs and maintenance that consume a lot of ink
If little ink is left, there may not be enough for large-format printing, head cleaning, and maintenance, which require a
lot of ink. In this case, replace or prepare to replace the Ink Tank before maintenance.
If a message for ink replacement is shown on the Display Screen
When ink runs out, the Message Lamp flashes, a message regarding Ink Tank replacement is shown on the Display
Screen, and printing is disabled. Replace the Ink Tank at this point.
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iPF670
User's Guide