If you receive one of the following error codes carry out these instructions.
•540 Toner Sensor Error, Color:Yellow
•540 Toner Sensor Error, Color:Yellow
•541 Toner Sensor Error, Color:Magenta
•542 Toner Sensor Error, Color:Cyan
•543 Toner Sensor Error, Color:Black
The C3400 Colour Laser printer contains four image drums: cyan, magenta, yellow and black. 1. Press the cover release and open the printer’s top cover fully.
2. Note the positions of the four cartridges.
1.Cyan cartridge
1.Cyan cartridge
2.
3.Magenta cartridge
4.
5.Yellow cartridge
6.
7.Black cartridge
8. 
3. Make sure the Toner Cartridge in question is correctly positioned and the right hand clip is pushed back
4. Holding it by its top centre, lift the image drum, complete with its toner cartridge, up and out of the printer.
5. On the Right hand side of the toner look for a sensor patch, make sure this is not dirty. This patch may be different depending how old your consumable is. If the patch is dirty it can be cleaned with a soft object such as cotton wool.
Now look inside the printer opposite to where the sensor patch would sit. There is a black square with a sensor located inside. Also check to make sure this is not dirty.
6. Replace the drum and toner, and close the printer cover.
Now look inside the printer opposite to where the sensor patch would sit. There is a black square with a sensor located inside. Also check to make sure this is not dirty.
6. Replace the drum and toner, and close the printer cover.
