Oki C9600/C9800:Fatal error code 133

My OKI C9600 printer has problem related to led head with error code 133. This error msg indicates Cyan led head is failed.
led head bar

There are some reasons that leading to this failure. One of them  might be caused by drum. If drum is dirty or  is overflown by toner.
So you may test C Led head to know if it is OK. How to test ?  Try changing with  another Led Head such as Y,K, M.
This is the way I did, and my printer is OK now.