K-Bus woes

[Riba]

Hello all,

I could use some feedback here. Few months ago I got the common problem with Nav/radio stopped working along with the dashboard turn signal indicators. I did my homework and it is clear that the problem is with the K-Bus.

Sometimes the radio and indicators would come back to life for a short while and I thing I see the radio flashing sometimes when going over speed bumps or rough road, so I suspect there is a weak connection somewhere causing all this.

I am having problems troubleshooting this though. I got to the K-Bus junction point behind the glove compartment and tried to disconnect one wire at a time to try and isolate the culprit. I even disconnected the battery after each step, but this got me nowhere. Radio and indicators remained dead in every case. I do have a diagnostic cable that hooks up to ODB plug, is there something I can use to diagnose this? My next step is to attack the K-Bus with oscilloscope and see what is actually going on here.

Any other ideas I might have missed?

Thanks!!

[80stech]

It looks like the LCM, radio and instrument cluster are all close together on the K-bus line. Taking off one wire at a time is useful if you suspect a short but I think you more likely have a poor connection somewhere, probably where the connector goes into one of the modules so even if you did put a scope on the K-bus line you probably won't be able to pin down the problem. Might be time for good old fashion wiggle and tug ??

[Riba]

But even then eliminating the culprit from the bus should resolve the symptoms...unless there are multiple failures, or maybe one of the modules which provides master power to the bus? Yesterday I inspected the wiring behind the instrument cluster, I will check the nav and LCM wiring...but it can be any of the connected modules if I am not mistaken, and the symptoms are usually always the same. Having the scope connected will probably help while doing the wiggle & tug at the same time. Sigh...

[80stech]

I should have said close together on the "same branch" of the K-bus.
I am assuming you have a nice diagram of the K-Bus? If not. maybe somebody could post that if they are watching?? Since you disconnected modules at the hub to eliminate them, and you still had no signals, I would think the problem would have to be at the kombi or LCM.

[Riba]

I do have a diagram, but my understanding is that they are all connected to each other on that comb type junction behind the glove box. I will know more once I actually check the signal there instead of working blind. I will share the findings if they turn out to be useful.

[80stech]

Hey it looks like there is an I-bus that might be involved? Not a lot of info on how the signal indicators actually work so this will be interesting.

[Riba]

I-bus and K-bus are essentially the same thing, the difference is the model in which it has been used. E53 is using a K-bus. Fairly simple thing using serial communication at 9600kbps.

[itsbrokeagain]

My DSP amp caused this same issue in my E39. I unplugged the sub and the amp, my navi/turn signals stopped going on the fritz and everything returned to normal. However my radio and CD changer are now both silent.

I will most likely delete the DSP anyway and start with a fresh system and separate amps.

[Riba]

Yes, problem is it can be any one the dozen or so modules that are connected to the bus. In my case the weird thing is that I was unable to isolate which one it is by using the common troubleshooting procedure, so I could be dealing with a combination of things. Lucky me.

[Riba]

Well, in the interesting turn of events I might have found the culprit today, completely by accident.

Actually few days ago I noticed that radio came back to life briefly as I was leaning over the center console to pass something to my son in the back seat. I thought it was a coincidence back then but now I know it was not. Today the radio turned on when I opened the center console compartment and that got me wondering. True enough, radio and turn signal indicators stopped working every time I closed the lid, and sprang back to life when I opened it. Of course, it must have been the useless mobile phone module located in there that was messing thing up the whole time.

I also recalled that last year I noticed that the spiral cord used to connect the phone used to get uncomfortably hot so I decided to disable it altogether. After a quick research I removed the fuse #73 back in the trunk. I have put the fuse back in place and now it seems everything works with the armrest open or closed.

Now I would suspect this immediately but I removed that fuse back in June, and the problems started in October.

Oh well, hopefully this info helps someone in the future.