E70 X5M DME NO COMMUNICATION - ECU FAILURE?

[yassa]

G’day I recently purchased a E70 2011/12 BMW X5M 4.4L TT,

The engine was just pulled and rebuild by a reputable specialist in Brisbane, QLD. After 2 months and over $18K the car was ready, so I thought… 950KMS after collection I experience an issue with the TCM where the car displayed DSC and ESC lights prior to stalling out. The gearbox was still engaged in gear so the ECU inevitaby prohibited me from cranking over. I was unable to engage/disengage the handbrake or put the gearbox into P or N. I scanned the car with a snap-on scanner where I noticed that there was no communication to the DME or TCU. I manually placed the gearbox into N via the bottom of the trans housing and manually released the electronic parking brake - to have the vehicle towed back to the shop.

The diagnostic from the shop was “a short which blew the gear selector fuse”. After a fuse replacement we had communication with the TCU and all transmission related computers however, nothing from the ECU/engine electronics.

We have power to the ECU, but the car just won’t fire/crank whatsoever, as if there was no ECU to begin with. Before biting the bullet and sourcing a new ECU I thought I’d try my lucky on the forums. I’d hate to spend thousands on an ECU + coding only to find that the issue was related to a ground/another contributing factor.

There doesn’t seem to be any precedents/similar issues on forums, so here we are. Has anyone experienced anything similar or know anyone who has? I’ve tried to be as comprehensive as possible, however may have missed some bits and bobs. Any help is greatly appreciated!

Cheers.

E70 X5M DME NO COMMUNICATION - TCM/ECU FAILURE?

[X5Sport]

That’s not good! Not seen it reported on the Forum, but the X5M is a rare beast on here.

My initial thoughts are that given the transmission and engine controllers talk to each other, a short could have put volts on a line at a level they shouldn’t have been and blown an input on a pin of the ECU. A BMW shop with the right diagnostics may be able to help narrow it down.

If it is that then the wiring itself needs a careful end-to-end check as well as an open-circuit or short to any other wire check carried out.

Coding the ECU by BMW should be straightforward as they hold the OEM map for the cars on servers in Munich so as long as no options have been added or removed the ‘as built’ map could be reloaded. Not sure about your part of the world, but for EU cars, if the car was connected to dealer diagnostics and the map didn’t match the factory, a new version could be downloaded into the on board memory and could overwrite any remap!

[Leslie]

Not x5m specific and quite possibly way of the mark but I wonder as you had dsc and esc lights just prior is it something to do with a bad ABS module which is now causing some comms fault and stopping communication with the engine ecu . maybe unplug the abs unit to remove it from the circuit see if it makes any difference ?

[yassa]

Thanks for the input gents, I can't see any physical damage/burn marks on the ECU pins nor the connector. I would have thought the DME fuse/relay would have shorted before damaging the unit itself? One thing I did forget to mention - immediately after the car stalled out, when I tried restarting I would get an assuring "click" from what sounded like a starter motor/relay? That is no longer present at all. I have sufficient voltage as the front of the engine bay so it doesn't appear to be a grounding issue like others suggest...

Leslie - I didn't think to check the ABS module... I wouldn't think that would prohibit communication from the DME module altogether?

[Leslie]

They are all linked by canbus now so one bad module can drag down others till its removed form the circuit , its just the fact it appears to have started with the abs circuit and you lost power like the traction control was causing the power drop till it stalled so might be relevant . It may well have nothing to do with it and that was just a symptom of something else .Is the gear selector working ok now as 30 amp is a big fuse to blow without causing any damage plus unless the engine ecu can see neutral it wouldn't attempt a start ,maybe it can see it but isn't reporting back ? The fact it did click is good but if it clicked it should really have spun over if you had sufficient power , have you had the starter out for a look/test as a short here could certainly do some damage . Suppose you could test of 12v is being sent down to the starter relay when the button is pressed? The heavy battery cable in the engine bay has a habit of working loose where it has joined too been a few reports of that on here so worth a check.
Id say all this could well have come from the engine being removed only a short while before , id be checking all cable around the exhaust system for scorch marks in case something was touching where it shouldn't and has melted/worn through . Something caused the short it didn't blow the fuse by itself so id be expecting it to blow soon again when conditions are right . Even a door handle I was reading can cause a non start these days (comfort access )

[yassa]

UPDATE: The car now cranks/turns over but won’t start…

Notes:
The engine cranks over resiliently but no spark or fuel (yet to pull the plugs to verify)
The fuel pump is constantly priming/circulating fuel when the car is in auxiliary

As mentioned, the gearbox has been manually placed into neutral and the car seems the register this (via the gear selector and dash).

I’m still getting no communication from the DME. CAS and DME relay are working as it should and there is sufficient ground. Everything is pointing towards a faulty DME unit, but I don’t want to bite the bullet without 99% certainty. As you implied, it doesn’t make any sense to just ‘fail’ on a regular commute with usual conditions. The battery terminal is secure, and I am reading 12V at the front of the engine bay and from the starter and all diagnosis has been done whilst connected to a tender/trickle charger.

I’ve replaced the battery in the and checked the logic board for damage. The comfort entry system can register the presence of the key and I have no codes relating to the CAS. I’m at a loss for words, seems like an over-engineered system to me.

[Leslie]

Not sure what else you could check they certainly are very complex nowadays what was wrong with the starter it wasn't cranking before ? If its cranking now the conform access must be ok. Maybe there is somewhere you can send your ecu for testing ?

[yassa]

I've towed it to a specialist and they've found the wiring harness to have been wired incorrectly by the shop, causing it to rub on the steering column which likely shorted the ECU. We've bench tested the ECU and are not getting any communication which indicates the unit is likely fried/damaged.

[Leslie]

Well at least you have found the cause of the short it seems as putting a new ecu on without finding that would be asking for trouble and a repeat of the same damage, not much space in there so critical all the wiring is clipped in to avoid just that issue. I don't know how easy it is to remove the cover but it might be worth a look if only too see how if there is any visible damage on the boards before splashing out on a new one. Id expect too see something given the fuse that blew