Canon CLC 1120 Service Handbook page 233

Code
• The toner concentration sensor is faulty/
E020
soiled.
• The developer inside the developing
assembly is not stirred properly.
• The sensor is subjected to stray light
(no cover, front cover open).
• The photosensitive drum has
deteriorated.
• The toner concentration sensor is faulty.
• The developer inside the developing
assembly is not stirred properly.
• The sensor is subjected to stray light
(no cover, front cover open).
• The photosensitive drum has
deteriorated.
• The window of the toner concentration
sensor is soiled or scratched, or the
protective sheet is soiled.
• The photosensitive drum is soiled (e.g.,
cleaning fault).
Cause
CHAPTER 5 SELF DIAGNOSIS
Timing of detection
xx24 At time of setting initial
data (as during
installation), the result of
averaging five retry
samplings of PT-SIG-M/
C/Y levels is '683' or less
or that of PT-SIG-K
levels is '305' or less.
xx30 At time of setting initial
data (as during
installation), the result of
averaging samplings of
SGNL-M/C/Y levels is
'859' or more.
xx31 At time of setting initial
data (as during
installation), the result of
averaging samplings of
REF-M/C/Y levels is
'930' or more.
xx32 At time of setting initial
data (as during
installation), the result of
averaging the first
sampling of PT-SIG-M/
C/Y levels is '930' or
more or that of PT-SIG-
K levels is '550' or more.
xx33 At time of setting initial
data (as during
installation), the result of
averaging samplings of
PT-REF-M/C/Y levels is
'859' or more.
xx34 At time of setting initial
data (as during
installation), the result of
averaging five retry
samplings of PT-SIG-M/
C/Y levels is '749' or
more or that of PT-SIG-
K levels is '371' or more.
5-5