konica C360 colour copier error code (C-255B)

[zawmyo201210]

My konica open start running C-255B error code show. So I am change yellow TCR sensor is not fix.
My machine Service mode Level 1 History from,

C - 6.1%
M - 6.0%
Y - 0.0% ❌❌
K - 6.3%

Please suggest what else to do.

[Synthohol]

replace the developing unit?

[zawmyo201210]

replace the developing unit?

I haven't done the developing unit replacement yet.