Dem communication problems

[Mick82]

Hi all new to the forum. I have a 2007 xc90 d5 185 bhp with 192000 having a problem with the dem module not communicating with vida just wondering if any body else had the same problem. Also the mechanic said it could be the pump but I've tested the pump when my original module went down and it was fine run 12v to it and it fired up but could a dodgy pump prevent Vida from communicating with it any advise would be gratefully appreciated thanks in advance.

[100K+]

I has an issue with my DEM on my V70 AWD R a couple of years back. In my research I found this :-

4. If the driveshaft is spinning, access the Differential Electronic Module (DEM). If there is no communication with the DEM, check for power on the Blue/Red wire, ground (Brown and Black wires) and network integrity by checking resistance between the Green and White wire. With the battery disconnected, there should be 60 ohms between the two wires.

Having researched my fault - no 4 wheel drive with DTS DEM0005 I did the above

There is battery voltage to pins 1+2 on the DEM connector, and 60 ohms resistance between pins 7 & 8 Canbus ( Battery disconnected - this I read is correct)

Before spending big money on fixing the issue,( I'ds be surprised if the AWD still worked) I'd consider removing the DEM and sending it to Volvo Diagnostics in London. Speak to Lucus, he has done many good turns for members here. Advertises in traders section. Personnally I'd bank that water has gotton into the DEM electrics and its U/S. fortunately Lucus can supply 2nd hand reconditioned units.

Good luck

Cheers
Bob

[Mick82]

Hi thanks for reply my unit is a recon conditioned 1 my original unit didn't communicate either when that went down but just put it down to the module that had failed as I don't know slot about these units gonna get under car tomorrow with multi meter and see what happens. Am I right in saying that num 7 and 8 pin are the ones that let the dem communicate to the system?

[SwissXC90]

Originally Posted by Mick82

Hi thanks for reply my unit is a recon conditioned 1 my original unit didn't communicate either when that went down but just put it down to the module that had failed as I don't know slot about these units gonna get under car tomorrow with multi meter and see what happens. Am I right in saying that num 7 and 8 pin are the ones that let the dem communicate to the system?

So your diagnosis was guessing and throwing parts at the car?
That's never a good methodology.

Find the root cause first, and then order parts.

You need to check if CAN bus communications (and power and ground) are present at the DEM, before you make any decisions about where the problem lies

And you need to be using VIDA to check for communications to the DEM....

[Mick82]

No I wasn't guessing actually when my original unit went down I came on the forums to research then had the car put onto Vida it wouldn't communicate then either so after a bit more research took the dem off and sent it off and found out that it was burnt out. So order a recon unit changed the oil and filter put the new one on it worked for a couple of hours then blew the fuse had it put back on Vida still won't communicate. I've come on here for help not to have snotty reply's off ppl

[Mick82]

Cheers Bob I will do that

[SwissXC90]

Originally Posted by Mick82

No I wasn't guessing actually when my original unit went down I came on the forums to research then had the car put onto Vida it wouldn't communicate then either so after a bit more research took the dem off and sent it off and found out that it was burnt out. So order a recon unit changed the oil and filter put the new one on it worked for a couple of hours then blew the fuse had it put back on Vida still won't communicate. I've come on here for help not to have snotty reply's off ppl

The DEM doesn't "burn out" for no reason.
The DEM doesn't blow a fuse for no reason.
You have to find the root cause that cause the burnout and caused the fuse to blow....

If the new DEM board also failled with the same symptoms, then you need to figure out what is going on.
What electrical part of the entire DEM remained in your car, when you removed the DEM?
Did the pump remain?
Does the pump work? Have you actually tested it?
Is it jammed / failled / overloaded? If so, that is what is causing the DEM circuit board to fail, and the DEM circuit board failure is simply a consequence of DEM pump motor failure.

Remember, the helpful people on this forum such as myself who invest personal time to provide feedback to you get very frustrated when only a partial picture of the fault and the actions taken is painted.

If you invest the time to fully describe the failure symptoms, and what actions you took and how you reached you decision that the DEM was bad, that would save all of us a lot of time and help you to reach a resolution faster.

I trust that you are able to see that my response is actually intended to help you, but you also have to help me and the other readers with a proper descriptive post about what you have done so far.

[100K+]

Originally Posted by Mick82

Am I right in saying that num 7 and 8 pin are the ones that let the dem communicate to the system?

Yep that's the pair I read about, and the ones I tested. Remember to have the battery disconnected for this test.

Originally Posted by SwissXC90

And you need to be using VIDA to check for communications to the DEM....

+1 on this too. without VIDA I would never have got to the bottom of my issue. And even with VIDA because I was not an experienced user it took a while, and help/chat with lads from here and other Volvo sites.
Did you use by chance BBA Reman??

Good luck

Cheers
Bob

[pumpkinhook]

I have read this thread (and others) and tried the suggestions posted to resolve my AWD not working. I say that it is not working as the driveshaft rotates when front wheel lifted & rotated, all wheels spin when all off the ground, but when I stomp the accelerator from standing start - the front wheels spun, nothing from the rear tires, slip indicator flashes.

I replaced the differential filter, pump, & fluid. Same tests as above, same result. I even replaced the pressure sensor (from junkyard).

I went through the DTS codes: DEM stated "Not Started" and did not change during a test drive. I have not checked voltage to the DEM via the harness connector (tomorrow morning), fuses are good. Does the message "Not Started" mean that the DEM is bad (if voltage present at the connector)?

Thanks.

[100K+]

Originally Posted by pumpkinhook

I have read this thread (and others) and tried the suggestions posted to resolve my AWD not working. I say that it is not working as the driveshaft rotates when front wheel lifted & rotated, all wheels spin when all off the ground, but when I stomp the accelerator from standing start - the front wheels spun, nothing from the rear tires, slip indicator flashes.

1) Front wheel off the ground and front to rear drive shaft rotating is normal behaviour. Its when the front wheels are on the ground and the drive shaft can be rotated you have a problem, but not at the DEM but the angle gear or collar drives.
2) If you can prove the pump is good by use of a 9v radio battery, the oil in the DEM is clean, the solenoid can be seen to operate again using a 9v battery, the "fail" points are basically down to two items - Pressure switch or DEM failure.
I have read instances of both.
However,
the DEM unit is located in an exposed position and appears to be susceptible
to water ingress. I would get your DEM checked out before spending more money, and if you intend keeping the car get a DICE/VIDA setup.

Good luck

Cheers
Bob