The PIXMA MG5420 must have all of the inks installed and contain ink for the unit to able to print.
If you are experiencing a "Low Ink" warning, you will still be able to scan, but not print.
If you are getting a "Ink Out" error, you will not be able to use the unit until the ink is replaced.
These precautions are in place to prevent damage to the printer from occurring if printing with no ink is attempted. The printer uses the ink to cool the printhead during the printing process. If no ink is present, the printhead could be damaged or the unit would require service.
"If you are getting a "Ink Out" error, you will not be able to use the unit until the ink is replaced."
Why not? Why can I not scan a document without ink? Scanning to a digital image does not require ink or printheads. Is it just bad or lazy programming or is there some real reason?