Dell C2660dn User Manual page 284

6 Open the top cover.
7 Put your fingers through the loops on both sides of the transfer belt unit, and then pull it out.
CAUTION:
If you cannot pull out the unit from the printer, make sure that all of the above procedures are performed
properly.
8 Clean the CTD sensor (as shown) with a clean, dry cotton swab.
282
Maintaining Your Printer