no power at the DME, not bricked!

[Conday24]

Hello, I'm hoping someone can guide me in the right direction with this customer car. Six months ago, I did an engine replacement on a 2012 E89 Z4. The swap was fine, and I've done a few BMWs before. However, after getting the engine back in, it would crank but not start. I'm not getting power to the DME. I have power from the battery to the junction box, but a handful of fuses that should be hot are not. I've checked all my fuses and connections multiple times, but still can't find the issue.

I sent the DME , CAS and the key off to be verified, and it was confirmed that I didn't brick the DME. However, I did brick the FWM (Footwell Module) during the engine removal or installation process. I sent it out and got it reprogrammed.

I'm having a hard time with the schematics, so my question is: could my short be a CAN bus issue? Specifically, is the junction box module not getting the right input from the CAS (Car Access System) and Footwell Module?" with the DME off line , ISTA isn't being very helpful to me on this one, any input would be appreciated!

[B21]

What does ISTA say?

Problem with canbus is any failure anywhere on the network can drag everything else down..

[Conday24]

Yes, of course. Please forgive me. It’s been a few days since I touched the thing so might take me a second to recall everything but here’s a screenshot of what’s going on.

[B21]

So you have a major bus failure…what condition is the battery in..have you tried a fresh fully charged battery ?

If so then you probably have shorted the can bus / disconnected it somewhere

[Conday24]

I agree that there's likely a short or something unplugged somewhere. I recently replaced the battery and verified power at the junction box (fuse block) under the glove box where the BCM plugs in. The DME relay is also getting power. I did replace the fuse block, but not the BCM.

From what I recall, the BCM has a specific behavior when it comes to power cycles and sleep modes. I'm wondering if the BCM has a failsafe mechanism that could be triggered under certain conditions, potentially causing issues with the car's electrical system.

I'd appreciate any guidance on how to troubleshoot this further, especially considering the recent engine replacement and fuse block swap. Could the BCM be the root cause of the no-start issue, or is there something else I should be looking at

[Conday24]

With the DME offline, I'd expect to see BUS faults. Since the BCM isn't sending power to the DME, it's likely causing the no-start issue. With a new BCM arriving today,but yes the batter is fresh and fully charged

[B21]

Originally Posted by Conday24

I agree that there's likely a short or something unplugged somewhere. I recently replaced the battery and verified power at the junction box (fuse block) under the glove box where the BCM plugs in. The DME relay is also getting power. I did replace the fuse block, but not the BCM.

From what I recall, the BCM has a specific behavior when it comes to power cycles and sleep modes. I'm wondering if the BCM has a failsafe mechanism that could be triggered under certain conditions, potentially causing issues with the car's electrical system.

I'd appreciate any guidance on how to troubleshoot this further, especially considering the recent engine replacement and fuse block swap. Could the BCM be the root cause of the no-start issue, or is there something else I should be looking at

In these cases without full scope and the skills swapping modules is often the way!

[Conday24]

Well , unfortunately, the used BDM did not fix the issue. But honestly, I’m not even sure if the new used isn’t bricked.the part numbers are the Same, but there is a one year difference between the two. I’m not sure if it’s good or bricked. I know my issue communication ( D-cam or B-cam _L) from the BCM to the DME. Causing the no power to the DME The continuity on this two lines from those two points are good.boy was it a pain to finger out the pin out,I know there’s other things that tap into it. I’m still thinking the BDM is the issue. Is there anyway to determine whether one is bad or not? I really don’t want to sent it to the dealer but I’m about out of option.

[B21]

Originally Posted by Conday24

Well , unfortunately, the used BDM did not fix the issue. But honestly, I’m not even sure if the new used isn’t bricked.the part numbers are the Same, but there is a one year difference between the two. I’m not sure if it’s good or bricked. I know my issue communication ( D-cam or B-cam _L) from the BCM to the DME. Causing the no power to the DME The continuity on this two lines from those two points are good.boy was it a pain to finger out the pin out,I know there’s other things that tap into it. I’m still thinking the BDM is the issue. Is there anyway to determine whether one is bad or not? I really don’t want to sent it to the dealer but I’m about out of option.

Looks bad..I’m out of ideas..

[MRCW]

have you tried checking continuity on wiring harnesses?

I did an engine swap years ago and found I accidentally crushed a portion of a wiring harness that caused some DME issues... it wasn't as complicated as BMW but still affected the system.

good luck