You can replace the sensor which will be expensive or you can try a method that requires tricking the system by placing a piece of tape over the sensors on the ink cartridges.
Open the ink cartridge cover, which faces the front of the printer on the right side.
Pull down on the release lever and lower the ink cartridge door.
Remove the ink cartridges that are reported empty by the MFC.
Look at the end of the ink cartridge that goes into the MFC. Locate the clear section where you can see the remaining ink in the cartridge.
Cut a piece of electrical tape to size so that it completely covers the ink sensor on each cartridge.
Secure the tape over the sensor on the cartridge. You can use a pen or pencil eraser to push on the tape and further secure it on the ink cartridge.
Push the ink cartridges you removed in Step 3 back into the MFC. Lift the levers beneath the cartridges until they lock into place.
Close the ink cartridge cover on the outside of the MFC by lifting up on it.
Press "2" on the MFC, if prompted. This tells the printer that the old cartridges were not replaced with brand new ones.