With the help of google here is your answer
Your arm of cover sensor has fallen off'
It is the switch fallen to bits
THis bit falls off
How yours looks
How it should be, or can be if you put it together again.
It might be possible to snap the part back on without partial disassembly, or simply shove something in there to hold the sensor in the 'closed' possition (If you lose a finger or two using this method, don't blame me)
The lid sensor is a tiny microswitch that is on the main circuit board...there is a white nylon lever arm snapped onto the switch.
if the lever arm falls off (like mine did) the 'cover open' error will last forever.
This may (or may not) be possible do fix without some disassembly. This lever arm should stick up through a rectangular hole that's approximately 1/2" to the right of the print head (assuming print head is parked in the middle) and behind it.
Most likely if your lever arm has fallen off, shaking the printer gently upside down with the cover open will allow it to fall out.
Now if you are a dentist or a surgeon, snapping the lever bit back on is no problem without taking anything apart.
I am neither. For the brave (of foolish) ones who like to do surgery, here goes. Here's how I took mine apart....if yours breaks into a million bits, don't blame me.
0) unplug the power and take the scanner cover off.
1) release the 'kickstand' from the scanner by prying and squeezing it with pliers until the two prongs pop out (or crack and break)
2) detach the scanner hinges by prying/squeezing with pliers until they pop off (or crack and break). (CAUTION: read step 3 below first...don't just yank the scanner off without reading step 3)
3) Carefully unplug ribbon cable and other connector to scanner and set scanner aside.
4) remove screws at front of beige plastic part....pry at the back carefully and this will pop off....sending the screws flying if you left them loose in their little wells. Don't worry, there are only two of them that really do anything anyway.
5) Look towards the rear of the printer and you will see the circuit board and the 'hole' where you can see the sensor, and possibly your white nylon lever arm lying pathetically down in the bowels of the printer.
6) Retrieve and Carefully snap the nylon lever arm back on, and think nasty thoughts about the brainiac who designed that part.
reverse the above steps. Put at least most of the screws back in, or the front panel may fall off at a later date.
Take care to GENTLY plug the ribbon cable and the other scanner connector back in, making sure it's seated all the way. Try not to bend or kink the end of it, or it will be toast.
Good luck, and happy lexmarking.....