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Discussion Starter #1 (Edited)
did some searches, no one has really had this exact problem. I bought my 2000 M5 in May, the PPI revealed a bad head unit. I made the selling dealer fix it, they used a refurbished unit. It worked fine minus it wouldn't eject the tape adapter I used for my I-pod. Other than that is serves it's function, radio and I can play I-tunes through the tape player aux adapter. About a month ago, I noticed the sound was only coming through one side only when using the tape adaptor/i-pod. Radio sounds fine, however I would have to switch between tape and radio until I got a good signal. Right after that I would hit a bump and my cluster gauge lights would go off at the same time the head unit would stop working(pixel OBC still works fine) hit another bump or accelerate hard and they come back on. NOW the gauge lights never come on and the head unit stopped working completely, so I assume these are on the same Bus-line? Sounds like the head unit took a crap, so might start with replacing and see how it effects the cluster issue. Any thoughts??
 

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By "gauge lights", do you mean the backlighting that comes on when the light switch is selected to side lights or headlights?

If so, does other back lit stuff like door switches go out as well?
 

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Discussion Starter #3
just the gauges, speedo, tach, fuel and turn signal indicators all do not light up..everything else on the car works(accept head unit)
 

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just the gauges, speedo, tach, fuel and turn signal indicators all do not light up..everything else on the car works(accept head unit)
So you lose the backlighting on the gauges AND you also lose the two green turn signal indicators?
 

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Discussion Starter #5
yes, and on the way home I also get a check seat belt warning which has never happened before and tire malfunction warning..some weird stuff. The head unit still doesnt work, sometimes the back lighting will come on the head unit, but the screeen freezes up and nothing works on the radio
 

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While I am not an expert at diagnosing electrical problems (or any kind of expert at all, for that matter) when it comes to our Beasts, I would like to suggest one possible reason for your issues. I wonder if your light control module (LKM) is on the fritz. The intermittent lighting and cluster issues you are having leads me to think this. The LKM is located up front in the right side foot well area just ahead of the front door, behind the carpeting. Also, your radio issues may be related to your lighting problem, but it also could be a separate issue. Your "monitor" up front is connected to the radio module, which is located in the trunk on the left side in the same area as your CD changer (if you have one). The "monitor" can go bad but sometimes the radio module in the rear can go bad as well.

I know this doesn't solve or give a definite solution to your issues, but I hope it'll point you in the right direction. You need to get with someone who has the diagnostic equipment that can communicate with the different modules (LKM, ECU, etc.) such as INPA, etc.
 

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Discussion Starter #7
Thanks, I did a quick test with my autologic, k-bus faults in the lcm and cluster, however after clearing them all out I activated the cluster test and the I k-line fault appeared instantly. So I tried to get into the LCM and could not communicate, will replace the LCM next week and update
 

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Some comments on your problem - the backlighting for the gauges comes from the 58G circuit on the LCM. This one circuit supplies ALL the backlighting throughout the car. If you have WDS, do a search on "58G". Since you haven't lost the backlighting anywhere else, I would think this problem was just in the part of the circuit that supplies the cluster, not in the LCM. This circuit is all hardwired, no busses are involved according to WDS.

The LCM talks to the IKE module (in the cluster) through the I-bus. I suspect that is how the LCM tells the IKE to flash the green turn signal arrows. If the LCM is successfully flashing the actual turn signals, but not the green arrows, I would suspect an I-bus problem, not the LCM, although it could be the electronics in the LCM that generate and send the signal over the I-bus. Is that what you think the problem is?
Does the blue high-beam indicator on the cluster work?

That check seat belt warning comes from the air bag module through the K-bus to the IKE. That's two busses acting up associated with the IKE. Maybe the IKE is the problem?

Actually, because you've got problems with two busses AND a hardwired circuit, and it happened initially when you hit bumps, maybe it's a connector come loose.
 

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Discussion Starter #9
thanks, but I have lost all back lighting, the radio and NAV unit are blank, just pixels in OBC are the only thing that stays on. I rechecked faults again after clearing over weekend and just 2 were stored:
instrumentation bus(i bus)
fault code entry for internal fault in light module 155 times occurrence in 2 days
I also took out the nav unit in rear, disconnected AM/Fm receiver in rear, and disconnected the amplifier and the head unit, the problem is still there. battery tested good, thanks
 
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