The Canon MG4250 cannot physically see inside the cartridges to find out how much ink is left. The copper contacts on the outside of the cartridge contain the ink level information. It is not possible to reset the ink levels to full. If you refill your cartridge, the printer will always show an empty cartridge message.
You can override the empty cartridge message by holding down the “stop / reset” button on the printer for around five seconds. The printer should continue printing, and use any of the remaining ink in the cartridge.
If the printer thinks that both cartridges are empty, you will receive a second error message, and you will need to hold the button for another five seconds.
If the circuitry on the cartridges is actually damaged this process will not work.
Youtube Video: Override the empty cartridge message.
Youtube Video: Change Ink Cartridge