zitsky

I'm trying to troubleshoot what seems like an unusual problem. My COMAND/Nav sometimes "goes out" and I'll get a "Navigation cannot be activated" error message. By running diagnostics I can see that the D2B bus is open, but I don't know yet which component is defective. Here's the interesting part. Sometimes, if I reset the D2B bus, the COMAND HU will just power itself off. The main power button won't work but I can still eject and insert a CD into the single CD slot.

Could this problem be a (1) bad fuse, (2) broken fiber cable that only occasionally goes out, (3) bad COMAND HU or (4) none of the above?

I'll try replacing the COMAND unit if I have to but I'd like to eliminate that as a problem. I don't see why the HU would power off if the problem is just a bus error.

Skylaw

Most likely it is either a loose fiber optic connection or a bad component on the fiber optic loop. You can try the troubleshooting procedure at http://www.carstereohelp.com/mercedesFiberOptic.htm - it is generally applicable to any model, and to any complete failure of the fiber optics bus.

zitsky

Thanks. I'm going to order that D2B coupler from the dealer. I was out today and this happened again. I tried pulling the fuse for the COMAND unit (#64 on a W203, I think), but that seemed to have no effect.

Would you happen to know the part # for the fiber optic cable that goes from the back of the COMAND unit to the CD changer? I haven't been able to find it on the forum yet. I noticed a small cut in the insulation in my cable, either from the cable being bent or rubbing against something. I think that perhaps this cable is failing occasionally giving me the open ring condition, and therefore might need to be replaced.

Skylaw

I don't know the part number - and you could be exactly correct that the cut insulation is the cause, especially if the fiber beneath is nicked.

I would try the dealership.

Diesel Benz

Is the CD changer the only device on the fibre ring?

http://www.detali.ru/cat/oem_mb2.asp...SGR=347&SGN=20

zitsky

No, my car is fully loaded, so I have Tele-Aid (deactivated), CD Changer, Bose Amp, COMAND, and Phone (not connected/not in use).

zitsky

I've been trying, step by step, to isolate the problem with my COMAND unit. I'm starting to suspect it's the COMAND unit and not the ring.

Using the d2b couplers that connect the COMAND to the CD ROM changer, I was able to remove both the CD changer, and the phone/PSE from the fiber ring. So, now I should only have the bose amp, and the Teleaid on the ring. I'm still seeing the same problem, the HU won't power on or will show an open ring condition but I can still insert/eject CD's in the upper part of the COMAND. I'm also getting no sound which suggests there is a fiber problem. I still could try changing the fuse on the Bose amp.

It's possible that the fiber to the other components is broken, but it seems more and more likely that I have a bad HU. I spent the day dissasembling the COMAND unit. It's rather interesting, and I figured I have nothing to lose, since it doesn't really work anyway.

I haven't given up yet, but at this point, I really don't feel like spending almost $1,000 on either a new COMAND or an after market unit. I'm thinking that I could downgrade the stereo to one of the Audio XX units with tape/cd etc. Those are running only about $100 on eBay. Would I be able to keep the AUX IN connection for an Ipod? I think I'd be better off with a portable nav unit at this point.

Diesel Benz

So this is a W203 car, Isn't the navi processor actually integrated to the head unit? I cannot see how the sound issue then would be related to the Comand issue (perhaps it just has difficulties reading the MAP DVD?).

Have you checked that there light is going through the fibre ring, specifically reaching the HU (light appearing at the HU input fibre)?.

Why not use the D2B bypass connectors for the rest of the devices. If you don't have sufficiently many connectors, you could reconnect some of the previously bypassed ones and assume those are fine (although one never can be sure).

zitsky

I will double and triple check the fiber connections. On one occasion I couldn't power up the COMAND unit but noticed that it was trying to talk to the fiber ring. I could see the red light flashing from the fiber module on the back of the unit after I applied power. That suggests to me that it could just be a bad HU.

What is the absolute minimum configuration? I assume I have to keep the Bose amp or I will lose all sound, correct? Or can I run without it and just have less power going through the speakers? I thought I could disconnect TeleAid, which I thought was in the left side of the trunk. But I don't see fiber going there. Am I mistaken?

I have discovered that you can run the COMAND unit without the nav processor. The nav processor/CD drive is connected to the rest of the unit by two flat cables. Those can be disconnected and you can run it as a very expensive radio.

Diesel Benz

You should not get any sound if the Bose amp was disconnected, so that should be your minimum configuration.

You say you saw light coming from the Comand unit, you should also check that you have light coming back from the fibre to the Comand, as well as any other device connected to the ring.

Can you confirm the exact car model? Tele-Aid should have fibre connected to it.

zitsky

My car is a 2001 W203 C240 (manual transmission).

I found the Teleaid and Voice module under the plastic cover right behind the rear seats in the trunk. I could see that the voice module is still connected to the Fiber optic network. The Teleaid module is NOT connected on the fiber network but is connected through the copper connection. When I disconnected it completely I got 'Teleaid visit workshop'. The dealership obviously didn't remove it with the SDS (?) computer, they just removed it from the ring. That's pretty worthless if you ask me because I think it was already obsolete when I asked them to do the work.

I remember looking at the fiber coming out of the nav unit and not seeing any lights when I turned on power to the car. So, that would mean that the device next in line to the HU was not connecting properly. That might be the voice module or Bose amp, I'll have to check. It might make sense, because any time I have this problem I don't get sound. I've tried replacing the fuse on the amp, that doesn't seem to help. I guess if I have to replace the amp, then I might as well replace the whole #$%@! installation. I could try removing the voice module tomorrow and checking the remaining fiber connections for light when I turn on the car.

Diesel Benz

I guess I was looking at a combined Tele-Aid/cell phone control unit. The above sounds reasonable because Tele-Aid is supposed to work when almost anything else in the car stops working and it cannot expect the fibre ring to work when Tele-Aid is needed. After all it has its own speaker and the microphone signal is first entering the Tele-Aid unit. As long as it is not part of the fibre ring, it should not affect your missing audio issue.

Some units have a fuse of their own at the rear but the amplifier should not have any. Also your head unit should not have a fuse issue since it seems operational except no sound.

I'm afraid the car should be diagnosed with Star if you find all units powering up fine (did anyone suggest resetting each unit e.g. by pulling the fuse off for a while) and the D2B ring working OK.