It is not showing "CDC", it is showing "CD" when the pibus is not connected. I assume this is the slot loading CD in the head unit.
With CD changer connected, Mode cycles through Radio, "No Discs" (changer) and "No CD" (head unit CD).
Without CD changer connected, Mode cycles through Radio, and "No CD" (head unit CD).
With pibus connected Mode cycles through Radio, "TR04 CD1" (pibus spoof of changer?) and "No CD" (head unit CD).
Sounds like you have a 2005 onwards radio module mate (with the latest firmware), these replace the cd message with TR, maybe the PiBus is now not "seeing" the correct cd string and therefore not switching.
Looking at the PiBus code (I've commented the hex code on the left)
buf[0] == 0x68 && /* Radio Source */
buf[6] == 0x43 && /* C */
buf[13] == 0x34 && /* 4 */
buf[19] == 0x4c) || /* L */
(bufPos == 16 &&
buf[0] == 0x68 && /* Radio Source */
buf[6] == 0x54 && /* T */
buf[7] == 0x52 && /* R
buf[8] == 0x20 && /* "space" */
buf[9] == 0x30 && /* 0 */
buf[10] == 0x34)) /* 4 */
The short string seems to be correct, but the long string seems to be looking at the wrong code, I think it should be looking at (43 44 43 20 31 2d 30 34)
buf[0] == 0x68 && /* Radio Source */
buf[6] == 0x43 && /* C */
buf[7] == 0x44 && /* D */
buf[8] == 0x43 && /* C */
buf[10] == 0x31 && /* 1 */
buf[12] == 0x2d && /* - */
buf[13] == 0x30 && /* 0 */
buf[13] == 0x34) || /* 4 */
(bufPos == 16 &&
buf[0] == 0x68 && /* Radio Source */
buf[6] == 0x54 && /* T */
buf[7] == 0x52 && /* R
buf[8] == 0x20 && /* "space" */
buf[9] == 0x30 && /* 0 */
buf[10] == 0x34)) /* 4 */
clutching at straws though!!!
