Nikon D6 Reference Manual page 1129

D
Image Sensor Cleaning
•
Using camera controls interrupts any image sensor cleaning begun in
response to the operation of the power switch.
•
Image sensor cleaning may not fully remove all foreign matter from the
filter. Clean the filter manually ( 0 1078) or consult a Nikon-authorized
service representative.
•
If image sensor cleaning is performed several times in succession, image
sensor cleaning may be temporarily disabled to protect the camera's
internal circuitry. Cleaning can be performed again after a short wait.
Caring for the Camera
1077