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Discussion Starter · #1 ·
My 2002 beastie flattened its battery a while back, and when I brought it back the airbag light was on. I picked up a Peake reader and it tells me it's an internal error in the CPU (table 4, code F0). I cannot reset the light.

A coworker has done a lot of work on Z3s, and says they used to light up their airbag light when the battery died. He had to send people to the dealer to get it reset. Does anyone have a similar experience with the M5 system? I can't just stop by my local dealer, they're 250 miles from here.
 

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I have had this problem.

Some other threads I participated in:

First
Second
Third

I know the light can be activated by not disconnecting the Battery before disconnecting an SRS component. Presumably, like most modules on the BMW it seems, it could be damaged by any type of voltage spike, ESD, etc.

Hope this helps.
 

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Discussion Starter · #3 ·
Thanks, that's a start. I'm guessing it's not typical for an M5 (and other E39s, I assume) to throw the light simply from a flat battery?

It sounds as if the dealer can do a lot more. Hopefully they can resurrect it. It does sound as if a replacement CPU (assuming damage from an electrical surge) will require a trip to the dealer in order to be properly coded.

I didn't disconnect anything. The car simply flatlined the battery one night sitting outside, and when I brought it back the light was on. I don't recall if I jumped it or just put it on the charger until the battery was up again - most likely the latter.
 

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Discussion Starter · #6 ·
Yes, I've thought of that. The car doesn't continue to have battery problems, so it seems unlikely the problem would show up just long enough to drain the battery and then go into hibernation. It's been over a year since this happened, but I seem to recall the alarm acting up around the same time.
 

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Discussion Starter · #7 · (Edited)
Use the proper tool, get the code and reset per the code readout. Maybe it is a real problem?
I've got a Peake R5/SRS tool. The code is "Table 4, F0" which is an inoperative CPU according to the paperwork that came with the reader. It will not reset. Do you have a suggestion for a better tool? There is a shop locally with a J2434 pass-thru tool, but I don't believe that will address the airbag system.

Maybe it is a real problem, that's what I'm trying to determine. I have experience with exactly one M5, that's why I'm trying to determine if there are other factors I need to take into account while troubleshooting. It would seem I can't just buy a $300+ CPU and stuff it in the car without a visit to a dealer anyhow. I'm reasonably competent at both mechanical and electrical work, and they're over 250 miles away so I'd prefer to only make the trip once if possible.
 

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He maybe trying to say the same thing I am getting at. You may have a short in the car that knocked the system out. It either burned your cpu or its fusible link (read its path to ground) and is not a short any longer. Anytime I see anything like that I want to inspect the electric system in general. Now that you have said the alarm was acting up at the same time would make me more concerned. I picked up from one of the first posts mentioned a electrical issue burning the strap.
 

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I've got a Peake R5/SRS tool. The code is "Table 4, F0" which is an inoperative CPU according to the paperwork that came with the reader. It will not reset. Do you have a suggestion for a better tool? There is a shop locally with a J2434 pass-thru tool, but I don't believe that will address the airbag system.

Maybe it is a real problem, that's what I'm trying to determine. I have experience with exactly one M5, that's why I'm trying to determine if there are other factors I need to take into account while troubleshooting. It would seem I can't just buy a $300+ CPU and stuff it in the car without a visit to a dealer anyhow. I'm reasonably competent at both mechanical and electrical work, and they're over 250 miles away so I'd prefer to only make the trip once if possible.
Autologic or GT1 -
 

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Discussion Starter · #10 ·
There's a fusible link going to the airbag control unit? Good to know. I will check that out. Other than a brief episode of the alarm acting up and the subsequent battery failure, there's been no indication of a short in the car. The error is actually "internal error", which could plausibly be a lack of power to the computer. I'll unearth it and see what I can figure out. Inspecting the electrical system in general would require pretty much a complete disassembly of the car from what I can figure, this thing's built like a space shuttle. With no other obvious faults I'm going to focus in on exactly what's being giving problems.

Autologic doesn't give pricing information on their website other than financing options, so I'm guessing it's a bit rich for a typical home mechanic. $460 is a bit painful for the GT1, I wish I'd known that existed before dropping a couple of hundred on Peake tools. But it may end up being a preferable option to driving to the dealer.
 

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general inspection means just that. Other blown fuses, is the car going to sleep, draw on the battery, could something else not working etc. Those sort of things certainly not looking at every wire, ya that would be brutal. If you find something is not working or another electrical glitch you investigate that. Just rule out other things if any that are not correct.
 

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Discussion Starter · #12 ·
Yup, that's how you troubleshoot all right :) But the thing is, the car doesn't have any signs of other electrical malfunctions. It does have one bank of cylinders that's running rich, but that's a brand new trick it just learned and the airbag light's been on for around a year - so I'm going to call them unrelated.

I'm going to start by digging out the airbag computer and making sure it's got power, then take it from there. The basic stuff. Looks like there are no particular M5 foibles (other than the usual dependence on expensive proprietary electronic diagnostic tools) to expect, which is what I was wondering about.
 

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Ya true. Not everyone gets that. Bottom line is if you know your electrical system is all good then it is sort of time to go see one of those machines that Valley speaks of. First point I would make is once you know the basics are correct, then you have to look at every wire so to speak. Only way to do that is with a diagnostic scanner. If going to one of them the last thing you want to hear is that they can't finish because you have a weak alternator or something.

Most important thing is airbags will likely save your life at the speeds these cars travel, don't you think that hiring a pro to look at it might be worth it? If you make a mistake in exploring the system and blow a bag it will cost you ten times more.
 

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Discussion Starter · #14 · (Edited)
I'm not going to blow anything. I've worked around airbags for quite a while, they're not scary. People are willing to work on their own brakes, and a failure there is a guaranteed accident.

If I had a dealer that was less than 4 hours from here and didn't involve crossing two 10,000' passes, I'd probably have stopped in by now. I'm trying to do my homework before I commit to that. If anyone knows of a shop on the western slope in Colorado that has the diagnostic tools, I'm all ears.
 

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That's a pretty compelling point. Brakes are not airbags but I get it. Only point is brakes don't require the use of those expensive machines until you get into the ABS. I hope you find a way to do this, and post the results. It would not be the first time a complicated system was exposed. I would not even know where to begin without either wiring diagrams or a diagnostic computer. If you happen upon the diagrams for this system please let me know I would truly appreciate them.
 

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The system consists of a metal box with one plug on it and a number of sensors, etc. The module (the box) itself is heavily potted (at least mine was) and I do not see a repair as possible. I do not advocate "repair" but that is not what the posts I referenced were saying. Considering the fault definition, it all but directs replacement (and proper coding) of the Airbag Control Module. I am not sure what troubleshooting can be done.

-Josiah
 

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Discussion Starter · #17 ·
Well, if there's a fusible link on the power to the box and it's blown, that's worth checking. I don't know how a Peake reader would react if the airbag computer was non-responsive. It's quite possible that it would return an "internal error". It behooves me to find out.

The alternative is to take a day or two off work, drive 4 hours to a dealer, get a bunch of stuff installed and then drive 4 hours home. I'm a DIY kind of guy - the M5 is one of the few cars in my garage that I didn't actually build - so that's what I consider a last resort. I know I'm atypical for an M5 owner.
 

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I guess I am saying that there is no fusible link for the ACM as far as I know. A fusible link is used in high current/high temperature applications (like alternator or buss supply wiring) and functions by actually vaporizing a section of wire that connects source to load. This is done using small gauge wire which, in the ACM supply wiring application would have to be pretty small. There is a fuse for the SRS, however.

I also believe that a supply issue would manifest itself differently in regards to fault codes. I am thinking of the 'Supply Voltage' fault specifically.

Hey, I can't fix or troubleshoot your vehicle from here but I can tell you from my own experience and other anecdotal evidence that your ACM likely needs to be replaced and coded. Given your distance from a service station that can repair this likely fault I guess it could be worth taking a look.

-Josiah
 

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I recently heard a horror story where the passenger airbag went out (worked/exploded) while the guy was changing the battery.
what could be the reason to cause that, wrong wires, short, etc.? :eek7:
 

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I recently heard a horror story where the passenger airbag went out (worked/exploded) while the guy was changing the battery.
what could be the reason to cause that, wrong wires, short, etc.? :eek7:

The airbags use an explosive to deploy the bag that requires a very small amount of current to initiate the explosion. Changing the Battery could have caused a surge that could have set off the explosive. Seems a might unlikely this could happen by just changing the Battery. Surely it depends on the vehicle and the type of SRS control and architecture it uses.
 
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