My printer Samsung ML-1640 shows the following message: "Toner exhausted".
To fix this you need to power off the printer and open the front cover. Remove the toner and shake it from side to side a few times then put it back and start the printer. Everything should be OK, but if you encounter additional errors you might need to replace the faulty part. You can visit Samsung Parts distributor locator for the nearest distributor regarding Samsung components.
