Last time I left my M635CSI it was acting like a bitch, even with the new Miller Performance MAS installed. That part had no effect on the bucking, intermittent shutoff of the fuel pump solenoid that made the car undriveable at times. Searching for the OBC controller box under the dash I found a box which by all accounts is the OBC controller. I disconnected it and started the car, and voila, problem fixed. I took a picture of the part but I've never been able to post pictures on this board successfully. It has 4 different cables connected to it; a gray cable with a round connector, a bayonet style green connector, and two four-pin rectangular green connectors. The part number is 65 75 1 375 125 1 and has a BMW logo on it. It's made by Sachs. With this box plugged in, the car runs like shite. With it disco'd the car runs perfectly. Strange part is, the OBC still works. Well, everything except the average miles per gallon button which is stuck at 5.9 and which does not reset when you push the reset button. All other functions work.
It seems impossible for the box that I disconnected to be the OBC controller with the OBC still working, unless I'm missing something very crucial to the component.
Guilty part(y) identified
Moderators: GRNSHRK, ron, bfons
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corsachili
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euro24
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corsachili
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ScottAndrews
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corsachili
Well it's not all the way fixed. The car has lost power, though not nearly as violently nor as often, about 4 times since I unplugged the alarm control unit. Something is still amiss. What's strange is that I can't find the OBC control module. I don't think the box I disconnected has anything to do with OBC, but the OBC is still not functioning perfectly properly (i.e., MPG not working).
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ScottAndrews
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horsetan
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86GT635
That box is the obc box too. It does control the alarm system as well. I am surprised your car runs with out. It would also be a culprit of the fuel pump cutting out. When you set the obc alarm/no start code, it disables the fuel supply. I think your box may have some bad solder joints or shorts in it. It is a major part of the cars electrical system and has a lot of stuff inside of it. If the alarm is not part of your regimine you may be able to use a computer from a non alarmed car.
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ScottAndrews
There is no" OBC Control Module". There is the OBC Module (which is what you see in the dash), and there is an "OBC Relay Box". This is on Page 123 of the manual I sent you. It is located "under the LH side of the dash".
The relay box (probably what you removed) contains two relays. The coils of these are fed by Fuse 21. This fuse also powers the OBC module, the chime module and a few other things.
One relay in the OBC Relay Box, controls power to the "Board Computer Horn" which I assume is the Alarm siren.
The other relay in the OBC Relay Box controls the MAIN Relay which In turn controls the Fuel Pump Relay, the Motronic Ignition power and the injector power (high side is hot and the Motronic grounds the injectors to open them). This relay is controlled by the GN/BR wire from pin 11 of the OBC which goes to Pin 4 of C1 on the OBC Relay box. Apparently, when the CODE is correct, the OBC grounds the GN/BR wire, and this activates the relay thus powering the main relay.
Mind you, this is a US car setup (I don't have the Euro ETM). I suspect that the Euro version may also have some sort of additional security scheme, or perhaps this is the optional super alarmed version (I suspect this is the case). What this means is that there will be other things that can cause the main relay to not get powered (based on the alarm state).
If we use this theory, then the Alarmed version of the car uses a different OBC relay box, and this would explain the extra connectors. I'l bet the non-alarm OBC Relay box has just the two 4-pin connectors, and the other connectors go to other parts of the car. To confirm this, you can test continuity between the other wires that led to this box and the alarm key switch you referred to in the trunk area. I'll be one of the extra wires goes to that switch.
So what confuses me (you too I suspect) is that removing the OBC relay box should de-power the Main relay, and the car should not run.
It may well be that someone has jiggered the system to fix a code or alarm issue, and this fix is not stable. Pin 3 of C2 at the box should be the Start-Run bus. This should go to 12 volts when the ignition is on, and be cold when the key is off. Pin 4 of C2 should be cold (which we know it is not, or else the main relay would not work with the OBC Relay box out). Both Pins 3 and 4 of C2 are GN wire. Check to see if someone has shorted pins 3 and 4, or otherwise hacked into the green wire leading to Pin 86 of the main relay..hopefully with a flaky fix.
The fact that the system works with the box removed tells me that either the relays are fried, or someone has been jiggering the wires (my guess) to get the car to run without the proper code.
The relay box (probably what you removed) contains two relays. The coils of these are fed by Fuse 21. This fuse also powers the OBC module, the chime module and a few other things.
One relay in the OBC Relay Box, controls power to the "Board Computer Horn" which I assume is the Alarm siren.
The other relay in the OBC Relay Box controls the MAIN Relay which In turn controls the Fuel Pump Relay, the Motronic Ignition power and the injector power (high side is hot and the Motronic grounds the injectors to open them). This relay is controlled by the GN/BR wire from pin 11 of the OBC which goes to Pin 4 of C1 on the OBC Relay box. Apparently, when the CODE is correct, the OBC grounds the GN/BR wire, and this activates the relay thus powering the main relay.
Mind you, this is a US car setup (I don't have the Euro ETM). I suspect that the Euro version may also have some sort of additional security scheme, or perhaps this is the optional super alarmed version (I suspect this is the case). What this means is that there will be other things that can cause the main relay to not get powered (based on the alarm state).
If we use this theory, then the Alarmed version of the car uses a different OBC relay box, and this would explain the extra connectors. I'l bet the non-alarm OBC Relay box has just the two 4-pin connectors, and the other connectors go to other parts of the car. To confirm this, you can test continuity between the other wires that led to this box and the alarm key switch you referred to in the trunk area. I'll be one of the extra wires goes to that switch.
So what confuses me (you too I suspect) is that removing the OBC relay box should de-power the Main relay, and the car should not run.
It may well be that someone has jiggered the system to fix a code or alarm issue, and this fix is not stable. Pin 3 of C2 at the box should be the Start-Run bus. This should go to 12 volts when the ignition is on, and be cold when the key is off. Pin 4 of C2 should be cold (which we know it is not, or else the main relay would not work with the OBC Relay box out). Both Pins 3 and 4 of C2 are GN wire. Check to see if someone has shorted pins 3 and 4, or otherwise hacked into the green wire leading to Pin 86 of the main relay..hopefully with a flaky fix.
The fact that the system works with the box removed tells me that either the relays are fried, or someone has been jiggering the wires (my guess) to get the car to run without the proper code.
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donudel
IIRC, the OBC alarm only disables the start signal to the Motronic. No connection between the OBC and the fuel pump that I've found.86GT635 wrote:That box is the obc box too. It does control the alarm system as well. I am surprised your car runs with out. It would also be a culprit of the fuel pump cutting out. When you set the obc alarm/no start code, it disables the fuel supply. I think your box may have some bad solder joints or shorts in it. It is a major part of the cars electrical system and has a lot of stuff inside of it. If the alarm is not part of your regimine you may be able to use a computer from a non alarmed car.
Don
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donudel
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[email protected]
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- Joined: Sat Apr 10, 2021 2:40 pm
- Location: canada
Re: Guilty part(y) identified
Thanks Very Helpful