Where is the lever on the cover open sensor

Follow the steps below to clear the "Clean Sensor" error message.

1. Open the front cover of the printer (cover D).
2. Slowly close the cover again. This action will move the lever shown below and clean the sensor.
   
3. Open and close the cover several times. Once the front cover is left closed the printer will start to calibrate.

Once complete, the error should no longer appear and the printer should resume normal operation.

Note: If the error message is still apparent after following the steps above, contact Epson for further advice.

This error message is displayed by the printer when paper is jammed in one or more locations. In such a case, users are recommended to remove the jammed paper from the specified location. The entire paper path must be checked for any pieces of paper. To stop the message, open and close the top most cover of the printer. Lastly, verify the flags and the sensors. If the problem persists, the cause of the error message could be a broken sensor or sensor lever.
http://h30434.www3.hp.com/t5/Other-printing-questions/Paper-Jam-Error/m-p/305772#M20513

An sc400 error means the toner mark sensor needs to be cleaned. Cleaning this sensor is easy:

Open the top cover and remove the cyan toner cartridge. You'll see a long black lever with a sort of handle that pokes upward -- slide this lever ONCE to the left, and then it should slide back into place.

Now replace the cyan cartridge and close the cover, and your printer should be fine. (If the error doesn't clear, turn the printer off and back on and it should go away.)

The printer displays a 'Cover open, please close cover' error message, even though the cover is closed.

This can happen if the lever on the cover open sensor is knocked off the switch assembly.

if you carefully remove the whole cover undo the 4 screws and gently prise the locating tabs away from body disconnect the small multiplug thing and the digital strip thing they come out easy but gently does it! then gently prise the hinges the hole scanner unit cover lifts off you will probably find the same as i did the small plastic sensor thing rolling around in there, fit this back over the sensor switch that you will see on the circuit board its very small but is there, poke it gently beforehand to check its moving ok, once the plastic bit is clipped back over your problem should not then exist! my cover open message went straight away, it drove me nuts trying to find out why! now my paper jams and cant find out why! hope this has been some help to you

I have fixed this problem on my 7820n printer by brother.

open the back door, then inside there will be a black colored other kind of like door that pulls back away from the roller. on this inner door is a black long thin plastic lever that runs from about the center of the inner door to the right. on the right end of it is a lever that slides along a curved increase on the right side wall. when both doors are closed this right end of the rod or lever moves up to close the gap between what is the sensor. this long thin plastic rod had snapped out of place and when i snapped it back in making sure the spring was correctly installed on the left end of it and the middle part of the rod slid correctly in its groove...the right end of the lever correctly closed the gap on the sensor (when both doors are closed) and the back door open error went away.

So that's how you really fix it!!!!

James Hilliard - Totally super awesome guy! hee hee

there may be any struck between the cover open switch which is in main board of the printer and the lever in the cover. open the cover and press the lever behind the cover. if the cover open message go away then do the same for 2 - 3 times after close the cover and try. even now he same problem happen make some arrangement or stick a paper bit on the top of the lever so as to enable it to press the sensor properly

Eject sensor actuator is too short or the main board is defective
Recommendation: Either the eject sensor actuator is not properly actuating the back cover
sensor, which is mounted on the rear side of the main board, or the
main board is defective.
open the back cover and look to see if the sensor is moving easily, if it is, you have a bad main board, if its not, the sensor is out of position.

i think the fuser sensor lever on your machine is damaged.
its the lever that you usually see when you open the cover the fuser unit.

This printer is same as Samsung CLP-500. So the problem is the same: Contaminated transfer belt sensor.

Do as follow:
Lift transfer belt assy from printer(Drop down back door 90 degree, press white button, lift top cover and release 2 locking levers, grab handle, pull the belt unit out), turn upside down & rotate plastic roller until small clear "window" appears along one edge of belt. Clean both sides of clear window with cotton bud. on same side as window, remove 2 screws securing flimsy plastic cover to gain acess to sensor, (follow red/black wires)remove a screw and pull out "U" shaped sensor(light transmiter and receiver), cotton bud and blow away dust on slits on inner surfaces of sensor. Reassamble and everything should be ok.If not, senser may be too contaminated, clean slits vigorousley with cotton bud, or maybe you just need a new sensor.

The theory is that printer detect transfer belt by transmit light through the clear "window". If either window not clear or sensor is contaminated, light will not reach the receriver part of the sensor, printer will report such errors.

Good luck.