98 m3, none of the speed functions on the on board computer work - average speed, distance until empty, mpg - nor does cruise control
speedo works. any ideas??
the alternator started overcharging and seems to have taken out my stereo, so I suspect that is potentially the cause.
I tried a used bcm and gauges, but no difference. Don't know if they worked or not before though. It seems like the problem would be in the dash gauges. Would love to see if anyone has a known good one I can try.
Nothing? Any recommendations on a good forum to try?
Wow, surprised the forum is so quiet, theres normally a few e36 experts around these parts.
being that the speedo works we can eliminate the sending unit in the diff. My thought is you are correct about the radio being the culprit, especially if the OBC stopped functioning the same time the radio stopped working.
There are multiple threads on bf.c where folks talk about the on board computer not working after installing an aftermarket head unit so perhaps yours also suffers that fate. below is one such thread. also that doubly answers your question. bimmerforums.com is my favorite place to check for e36 specific help.
http://www.bimmerforums.com/forum/showthread.php?1068228-OBC-Doesn-t-register-speed-or-MPG
yeah, I don't know without looking it up, but I think the signal goes: diff -> ECU -> Gauge cluster -> OBC/Cruise/etc, so that would seem that something either in or after gauge cluster is the issue.
I've had good luck with the bentley workshop manuals, they usually have detailed testing procedures for each component, including electrical ones. And wiring diagrams are awesome.
Holiday weekend is my guess, but would check the basics to include fuses and useable links, next would be put on a scanner and see if theres any faults in the dash. Good luck and keep us up to date.
I had found that thread before and most seem to address swapping obc's around.
A little more history - everything worked great for years. Pioneer head unit and cruise and obc.
Then my autozone alternator started overcharging after about 1 month. At the same time the radio stopped and I think/assume the cc and obc functions did at the same time.
The alt was replaced but of course the damage was done.
My understanding is that the problem should be after the speedo (whether in or out of the gauge cluster) and before the cc/obc (wherever the signal splits - assuming it does)
Perhaps my best bet would be a good manual, but I was really hoping someone more experienced than I with these guys might be able to point me to a likely culprit.
Alternatively, I'd love to try a known good gauge cluster. I have a spare of unknown history.
Speed sensing volume on the original stereo?
Hmmm. I'm not sure. The Panasonic didn't have it but I wonder....
It's not made sense to me that the overcharging alternator could take out the speed signal after the cluster but maybe the stereo did it somehow....
oldtin wrote: Speed sensing volume on the original stereo?
This is a really good thought. I bet the original stereo had it. Wonder if somehow that signal line is now shorted to ground or something, pulling the signal with it.
I'm still pulling my hair out over this....
I have removed the stereo and the factory plug and harness are uncut. An adapter was used for the stereo.
Can anyone confirm my suspicion that it is likely a wire(s) coming out of the gauges that talk to the cruise control and the Obc that would be causing this?? And if so, where would I look for it??
Does the E36 have the same I-BUS network the E39 does? If so, you could log into it and see if the VSS signal is there. If it's got one of those networks, a missing head unit shouldn't bork the speed signal as it'll be broadcast.
In reply to Keith Tanner:
I confess I do not know the answer to that. Unfortunately, if it does, I have not the tool(s) to log into it.
It acted like this before I pulled the stereo out as well
I didn't have the tools for that when I bought my E39 either. But I do now!
The E36 has no CANBUS. There is a speed sensor in the diff but if your speedo works it's getting that far. The radio and OBC are not linked - but if an over-voltage condition took out one then the it's reasonable to assume it took out something else. I cannot recall if the cluster feeds the OBC or they both split out of a small box behind the dash (that might be the E30... they all start to run together after a while).
But- I would chase the wiring to where the cruise gets the speed ref from - and bet fixing that fixes all the woes. If you google hard you will find a PDF of the wiring online.
I-BUS, not CAN. The E36 does have it according to Googles.
Does the mpg gauge in the cluster work?
But still you need to find the information path (wiring diagram) and follow it until you find the point that the info stops flowing.
If the information is on the I-BUS, it's not a linear path. It's broadcast into the network for whatever wants to listen. At least, that's my understanding. I've swapped out a couple of I-BUS components, and it doesn't really matter where you put them.
My understanding of I-Bus is that it is only used for entertainment/peripheral information transfer. Things like PDC, Nav, CD player, steering wheel controls, body control, and of course, the OBC. It does sound a little bit like there was a failure on that network.I think the ECM broadcasts that particular SPN and the other devices are just listening. the information must be there if it's getting to the cluster, unless the cluster broadcasts that particular piece of information.
Head units, in my experience, can be pretty sensitive to overvoltage. Many also have integrated protection that can be overcome by unplugging the connector (or pulling the battery lead) and letting all the caps discharge. 10 minutes has always been enough time, if that was my issue.
This is why I don't like troubleshooting data busses...
Some good info here, btw: I-Bus
I-bus is typically single wire, and only sends signals, so if you are getting some of the functionality that I-Bus transmits, it isn't an issue with the control unit itself, but the unit(s) affected. Are you getting functionality of any of the I-bus-fed features? Steering wheel controls, etc?? If it's all dead, it's most likely a cluster issue where I-Bus derives. Not exactly sure which pin it is or should be, but this diagram proved helpful for me to diagnose some unrelated electrical issues on my E36.
According to AllData, the VSS sends its signal directly to the instrument cluster which then outputs it on a single wire which is spliced into 7 different wires, one of which goes to the OBC, and one of which goes to the cruise module. That splice also leads off to the radio (gone), but also to the speed-sensitive windshield wipers and to the automatic climate control. So, if you can verify that the speed-associated functions of either of those are still working, i would assume the section between the gauge cluster and the splice is ok. If you cant verify the speed-related functions of ANY of that, I would go to the splice and check continuity between the associated instrument cluster connector and that splice looking for an open circuit. The splice is located in some kind of box just forward of the driver side strut tower, and all the wires attached to that splice are black with a white stripe. If there is no open circuit i would assume the output part of the cluster is somehow fragged and try a different cluster. I'm not sure how to directly verify that there is a signal coming out of the cluster on that line because i don't know what the signal actually is, but it's possible you could detect it with a multimeter set to measure either AC voltage or frequency (hz).
Anyone else read the title and want to answer "more fiber, less spicy food"? 
BMW Electrical Troubleshooting Manuals
These were not easy to de-cipher the first few times I used them. And they're not really that easy for me even now. BUT they are my only hope to track down electrical issues in my E36 chassis (which now runs a Ford EEC-IV for engine control and a TFI system for ignition/spark, as well as various other DIY sensor and monitoring devices I am adding over time).
Once you get the hang of it, you can read the circuit, find the sensors and modules, the wire routing and colors, and the locations of the connectors and nodes where you can tap into them.
Good luck.
In reply to Vigo:
Awesome. I am in Atlanta for a few more days but will check for this as soon as I return!
In reply to JBasham:
Much obliged. I will investigate these as well.
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