Hello all! strange thing seems to have happened. ihave a 2004 xj8 VDP with the premium sound system and rear entertainment. i haven't used used the car in a while since i got the "gearbox fault" message. then the radio had gone out last year. i was told that there was corrosion on the amplifier connector. but then the radio worked on its own for a while...and sometimes it will work all by itself for 20-30 minutes and cut out again. so i checked the posts, got some info on checking the amplifier and also self diagnostics on the screen. i did, no codes were stored. but, playing around on the menus, i did notice that my menu choices had been reduced by one...the rear entertainment/premium sound choices tab is no longer there. i have only 5 soft buttons not the usual 6. the diagnostics screen that allowed me to check the sub-systems seems to indicate that there is no rear cd changer or rear entertainment. it's like the car decided to revert to a more base sound system. so, what gives?
thank you in advance, william

 

There must be a problem with your D2B optical ring. It connects all audio components together in a ring like system - meaning signal from one component passes to the next. When the ring is disrupted somewhere the communication with all subsequent components is lost.

When your head unit starts it tires to do a "roll call" to see what components are connected to the system, because your car has an issue, it finds only a few of these, so your menus are incomplete.

There can be a few culprits:
- the optical cables connecting the components in the "ring" are disrupted somewhere.
- the "wake up" electrical signal is broken somewhere so some component(s) don't get the "roll call".
- one or more component is broken and does not pass the data downstream the ring.

What is odd is that you don't get any diag codes though. Anyhow it's a very weird system they use so pretty much only the dealer software can be used for diagnostic.

 

Yes for sure it's an issue with the D2B network, there are lots of connections in the black fiber-optic cables, if one of them gets loose then you'd have this sort of intermittent problem. Also if one of the modules drops out then you lose the whole network. Check all the connections for a start.

 

wow! thanks for the replies and information guys! that sounds what may be happening....to fill in more information, the car was rear-ended in summer of 2011. shortly thereafter, the nav didn't recognize the map dvd, had to switch out the nav unit (the insurance paid it for it and i got an undated dvd), then the radio would cut in and out, but the rear entertainment still worked. only once i had the 5 tabs show up, the usual 6 showed up after a period of non-use. last summer the a/c blower cut out, i used the car for several months with no a/c (in texas no less!) before i replaced the blower module myself. radio cut out about that time and didn't come back on until last weekend, and then it was only for two periods of 30 min only. to tell you the truth, ever since the accident. i really don't believe that these particular cars will ever be the same after repairs. maybe that is why my trusty standby is the '83 xj6?
cheers!

 

good morning! quick update...this morning when i turned the car on, it started and the radio turned on too...for 30 seconds! BUT, i did check the menu, and i had all 6 tabs there. the missing "rear entertainment" soft touch button was there. then, when the radio cut out again, the menu reverted back to the 5 tabs. so something is either loose or a short? is the nav system on this loop? if so, how can i bypass it to see if the other systems are working? how difficult is it to expose and check the back of the "head unit"? or expose the wire harness from the back amplifier?
thank you in advance, william

 

The Nav is connected to the loop. I do t think you can bypass it though as it may be the master unit. The Nav controls the screen, so there won't be much stuff to click if it's off.

 

Sound like you have an issue with your optical cables. If the cable is pressed too much it would conduct less light and you may get these intermittent issues. Also a cable may get dislodged form the connector and some of the light would get trough but not enough.

Merc dealers have a special tool that can measure the level of signal loss in the optical cable, jag may have similar tool.

 

thank you for the additional information. i'll definitely check it out. how does one remove/access the back of the head unit to check the connections?

 

There are a bunch of audio components in the trunk - your nav unit, the audio amplifier, CD changer and the link to the RES. Since the problem started when you were hit I would start there.

To remove the head unit you need to remove the center console. Find the installation instructions for the ACM module - a big part of that is gaining access to the head unit.

 

Guessing that the repair was not done at a dealership shop? Or if it was they missed damage to the fibre optics.

You may want to check in with the insurance company and let them know before you get too much farther along. If it was accident damage, they should pick up the repair tab.