Trans Fail Safe & Multiple CAN commucation failures

[Deansbimmer]

So here is a doozy, please post if you can share some helpful info as I work through this issue. 2002 X5 4.6is. Yesterday I went through and did a lot of maintenance that I'd been putting off. Installed all new:

L+R Front CV axles
L+R Front brake rotors & pads
L+R Front engine mounts
Front driveshaft flex-disk
Front differential fluid exchange
A/C Compressor replaced, system vac'd and charged.

Now.... After a couple of very brief driving cycles to bed the brakes and check my work, the car suddenly went into Trans Prog Failsafe and I hooked up BMW ISTA to see whats up. Immediately I noticed that the software would not "identify" the car- no communication to various modules. I manually entered the VIN and looked at the control tree and cleared all of the codes including the no-communication codes. All was OK for three more driving cycles into this morning when my wife and I went out for our Saturday morning coffee.

Same issue crops up with TRANS PROG FAILSAFE, and now no matter what I do I cannot get any communication with ANY module in the car, and clearing the codes results in the ISTA software immediately returning unable to communicate.

I find it extremely suspicious that this may be simply coincidental to the maintenance I did to the front, so am tempted to rule out a faulty module. Something I did must be causing a CAN BUS failure. Maybe I damaged a wire when lifting up the engine to replace the mounts?

Symptoms:
Engine starts/runs fine, with CEL for CAN timeout codes.
DSC/ABS Light immediately on start/run
Trans Prog Failsafe soon after engine start.
Instrument cluster's Tach/Oil temp/Water Temp/MPH gauges are inactive
Cannot communicate with any modules through ISTA or other stand alone scanners

Attempted Fixes:
Checked all fuses and relays. All OK.
All systems within the car seem to function normally.
OBDII port seems to be functioning with 12v present- ISTA will identify chassis type/prod date.
Alternator output shows 14.1-14-3v when idling. Batt at appr 13v when engine off.


Is there a relay or fuse in a hidden location that controls CAN communication? It is strange that I was able to reset the modules last night but not this morning.

Please post your thoughts!

[Deansbimmer]

The only control unit it will communicate with is the steering angle sensor. This control unit tree is innacurate (car actually has more modules equipped).

[Deansbimmer]

Update:
I let the X5 return to ambient temperature and went back to check status. ISTA was immediately able to identify and communicate with the car and its modules. I was able to clear the codes pictured above. After the vehicle re-test, I was left with only one code within the DSC unit, seen here as the 5A code for Brief Power Interruption. Apparently the module cannot be read due to the existing power loss.



I find it hard to believe but I suppose it is possible that I could be experiencing a DSC/ABS module failure, as coincidental as it may be. I may have jarred it just enough during the repair to finish off some of the internal contacts.


Now, from what I understand about the CAN BUS communication system, all units within each CAN network produce their own voltage through the network. With the IKE as the root unit and communicating to all CAN systems, if the DSC unit has an internal short across the CAN/H CAN/L, it can potentially disrupt all CAN communications within all networks. I'm not sure how feasible this scenario is but is my thinking on the right track?

I know that if the trans (AGS) does not receive its needed signals from wheel speed sensors etc it will go into TRANS PROG FAILSAFE, so again it leads me back to the DSC/ABS being at the center of the issue.

Could really use some feedback.

[Deansbimmer]

Judging by the fact that nobody here has even commented on this I'll assume that this was beyond the ability of anyone here to troubleshoot or even comment on. Kind of a let down.

Anyway, in case anyone ever reads this while experiencing similar issues... I rebuilt the dsc/abs module and everything returned to normal. Chalk it up to another Bosch 5.7 failure.

Thanks anyway, guys...

[deepblonde]

Thank you for the update,
how did you figure out it was the DSC/ABS module?

[Deansbimmer]

Originally Posted by deepblonde

Thank you for the update,
how did you figure out it was the DSC/ABS module?

It was an educated guess. When the car was hot, I couldn't communicate with any modules and everything was going haywire. When cold, I could at least connect to the car with ISTA, and could communicate with all of the modules except the DSC, which had the recurring 5A intermittent power loss failure. After googling, this is a common failure mode for the 5.7 DSC, so I sent it off to be rebuilt.

[jopecasa]

Originally Posted by Deansbimmer

Judging by the fact that nobody here has even commented on this I'll assume that this was beyond the ability of anyone here to troubleshoot or even comment on. Kind of a let down.

Most of us.......are under the SAV fixing our issues too and far away from the pc!

You're not alone......visit other forums and asked members out there.




I don't understand how a faulty DSC would affect the CAN and other modules.

But...It did fixed your issues and thanks for sharing.

Great work!

[Deansbimmer]

I had to read up on how the CAN system worked. It works at a low voltage with I/O data stream across a high/low parallel data line. If there is no voltage, high voltage, or a short across the high/low streams then it can basically paralyze the network. Since it's interconnected with every module, if there's a fatal problem within one module it will kill the communication to every other connected module.

Each module supplies its own power for the CAN line, so you can diagnose a module failure by disconnecting one module at a time. But as long as one module's CAN circuit fails and remains connected, you won't be able to see it in the network or communicate with it.

I don't know what exactly failed inside the DSC module, but it definitely was wreaking havoc with the CAN system.

[David.X5]

Cool. Nice to learn something.

But as an engineer, let me say that it seems like a crappy choice of architecture for the application!

[ray244190]

I have the same issues. In addition, I'm unable to lock the doors using the key itself. (Battery died in fob), and no A/C. I've read in other post about it being the same thing as you went through.
Where did you get yours rebuilt at, and I hope it was under 500 bucks.
Great post and great job.

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