I was not able to access the radio service menu for some time, asked question, read documentation, nothing helped, until today. I had tried ANY (ABSOLUTELY) ANY possible way to get into that menu. Holding the SELECT button, holding INFO button, selecting RDS and holding the right knob...nothing.
Yes, the answer is very simple, stupid me!
The problem comes when your navi doesn't know what type of radio unit it communicates to. I had some problems with the NavCoder and it couldn't read settings etc., so I could not know what type of radio unit was my navi set to use. I decided to recode it again with my proper radio model (which is C43 BTW) and voilą...Finally I was able to access the radio service menu by selecting INFO then scroll down to RDS press and hold for about 10-15 seconds the right round knob.
I hope this helps to those who have been pulling hairs out on this.