CAN Bus failures? Multiple control modules not communicating need help troubleshooting!

shaneb · Post by **shaneb** » 06 Apr 2019, 10:39

I replaced valve cover gaskets and other items last week (starter, PCV, etc).
About a week later - the remote fob, SRS, all drivers side door functions, climate control, radio and map lights, etc do not work.

I have checked all the fuses on the drivers side footwell, door well, and engine bay - none are blown according to my meter. I have no idea what to do or where to go looking for grounding issues or otherwise? Vida mentioned a startup procedure for re-connecting battery and getting the UEM working but the remote fob doesn't even work and when i disconnect the battery the alarm goes off?

When we disconnected the battery last week to do the starter and valve covers - the alarm did not go off, we also didn't put the key in position II when we reconnected it...maybe that's part of the problem?

Anyone have some idea what to check or physically where in the car it could be checked? VIDA mentions some pin outs to check with a meter but they require a 800 dollar breakout board apparently?

Attached is an image from VIDA to show the codes I am getting

: Annotation 2019-04-06 113337.jpg (78.51 KiB) Viewed 19921 times

Thank you in advance for any advice you may have, it seems most likely there is just one large connector somewhere that has broken loose or a ground wire got missed while doing work on the car but I haven't the slightest idea where to start, it seems clear to me its a wire on the CAN bus that has lost its connection but I do not know what route the CAN bus takes or where to go looking first.

Post by **RickHaleParker** » 06 Apr 2019, 12:07

All Signal missing DTCs.

1. Check for a blown fuse.
2. Pull the wiring harness connector on the CEM, clean connector and reconnect.

Post by **jimmy57** » 06 Apr 2019, 12:30

The modules offline are all behind the ICM which is also offline. Fuse 8 in the end of dash fuses is its fuse. Was anything done at thedio audio display unit. That cnnector being unplugged would take all those off line. Is the audio display coming on?

Key pos II battery connect has nothing to do with network. It is solely so you are at battery when everything comes up in the case that SRS has a serious issue and fired airbags. At the battery none can touch you.

shaneb · Post by **shaneb** » 06 Apr 2019, 12:44

jimmy57 wrote: ↑06 Apr 2019, 12:30 The modules offline are all behind the ICM which is also offline. Fuse 8 in the end of dash fuses is its fuse. Was anything done at thedio audio display unit. That cnnector being unplugged would take all those off line. Is the audio display coming on?

Key pos II battery connect has nothing to do with network. It is solely so you are at battery when everything comes up in the case that SRS has a serious issue and fired airbags. At the battery none can touch you.

I just checked, Fuse 8 at dash side is 15a and doesn't look blown/checks out with a meter.
To answer your question - the infotainment is not on.
I'm investigating how to remove the CEM harness and re-terminate it but nothing under there looks even close to loose or disrupted, I could see a foot making its way onto a cable and pulling it, maybe..

But your comment that if the infotainment gets unplugged - it will take everything downstream with it - makes me think I should pull this out next? If it dies does that mean everything behind it is dead, or only if it is unplugged it doesn't pass it through?

Here is a picture of RED or offline modules

: Annotation 2019-04-06 134154.jpg (52.08 KiB) Viewed 19905 times

shaneb · Post by **shaneb** » 06 Apr 2019, 15:02

I found something
I pulled the infotainment and climate control out and found two wires cut.
The two wires are obviously shorter than the rest in the harness and there was a piece of electrical tape, i have no idea how these would be so much shorter? I watched all the videos of this procedure on YouTube I could find, and no one else has a short pair of wires. But the tape seems normal.
I suspect I should splice these wires back and then put it all back together, but this is a serious mystery.

shaneb · Post by **shaneb** » 06 Apr 2019, 15:46

I temp spliced that stuff back together and tested it and the climate, keyless entry and radio came back up.
SRS Light still active but I'm going to do a proper splice, get it all put back together and erase codes with Vida then see where I am.

Thank you guys for the help so far. I'm at a loss as to how this could have happened, we haven't owned the car THAT long and we have never been in the dash before. There were two broken clips where the climate control screws at the bottom but every clip I've touched in this car has been easily broken so I may have done it.

Hopefully the next poor guy who googles SRS, Keyless, Radio, Air Conditioning and Windows broken finds this thing useful. 2008 XC90 V8

Post by **jimmy57** » 07 Apr 2019, 07:18

The green and white wires are the CAN communication wires. I can't think of any reason why you want to cut those. You can solder in some wire sections to extend those. I would use heat shrink to cover the solder splices. Those wires have a twist on purpose. In this area there are not a lot of wires so if you add wire and the spliced ones are not close to the others then the chance for any signal bleed is not going to be an issue.

shaneb · Post by **shaneb** » 07 Apr 2019, 07:27

As best I can tell this has never been pulled before. It’s strange. If it were a house I would say a mouse ate them. An inch was missing from them.

I expected it was a twisted pair serial comm or similar so I used a like type maintaining their twists with Sopoby heat shrink crimp connectors and a label back there for what I found and what I did.
Luckily, if it happens again, I hopefully know where to look.

Post by **RickHaleParker** » 07 Apr 2019, 07:37

One end of the wires look like they been cut (straight and clean) but the other end looks like it may of been chewed ( Rough and uneven).

The two wires are a twisted pair. The twisting reduces Crosstalk (electromagnetic induction) between pairs, which improves signal quality.

Post by **ggleavitt** » 08 Apr 2019, 12:52

Tidy mouse.

Low speed CAN, pins 3/5 are from the CEM, pins 4/6 are to the CCM.