Dell C1760NW Color Laser Printer - Manual (Page 197)

Maintaining Your Printer 195
Cleaning the Color Toner Density (CTD) Sensor
Clean the CTD sensor only when an alert for the CTD sensor is shown on the Status Monitor or operator panel.
1 Ensure that the printer is turned off.
2 Push the rear cover release handle and open the rear cover.
3 Clean the CTD sensor inside the printer with a clean dry cotton swab.
4 Close the rear cover.
5 Turn on the printer.