Replaced a rear diff in a friend's 04 xc70, here's how it went...

[Hamfist]

Update, just hooked negative back up after a day. All messages but brake failure are gone. However, now the tachometer dropped to zero and the dash says it's in park, but the shifter says it's in reverse. The engine revs in drive and barely moves, unless you select a gear. Reverse works fine. Speedo inop too.

Ugh, what now?

[Hamfist]

Update, just hooked negative back up after a day. All messages but brake failure are gone. However, now the tachometer dropped to zero and the dash says it's in park, but the shifter says it's in reverse. The engine revs in drive and barely moves, unless you select a gear. Reverse works fine. Speedo inop too.

Ugh, what now?

Think I found something. After researching the lost comm codes and p0571, I decided to check out the DEM on the diff. It's different that the original.

The used diff and DEM had lots of aluminum corrosion on the mounting surface, I cleaned that. Also, the used one had bent pins! Also was missing the copper windings the original had.

Installed original DEM, comm codes gone, but brake codes remain.

Disconnected battery first

[Hamfist]

Well, all comm codes gone, did a few test drives, no return of old codes. Lesson learned, disconnect batter before any work with electrical.

However I don't think the AWD is working. I came to a complete stop and jammed on the gas. Front tires spun forever and rears never kicked in! On the dirt and pavement, same result, then sometimes, I would repeat and it would take off with no spin.

Ugh, tomorrow is another day, I'll put it up on Jack's tomorrow and run it and see what happens.

[hoonk]

However I don't think the AWD is working. Front tires spun forever and rears never kicked in!

Did the haldex unit/DEM work before you replaced the Differential? Haldex/DEM failures are common and can be $$$ to fix. You can't really easily test the haldex electronics/clutch by running the car off the ground. The system gets confused if all the wheels are not turning at about the same speed and won't engage. This is where VIDA or a scan tool that can talk to the DEM is needed.

[Hamfist]

Did the haldex unit/DEM work before you replaced the Differential? Haldex/DEM failures are common and can be $$$ to fix. You can't really easily test the haldex electronics/clutch by running the car off the ground. The system gets confused if all the wheels are not turning at about the same speed and won't engage. This is where VIDA or a scan tool that can talk to the DEM is needed.

Yes, the AWD was working, but the old diff was howling, bad bearing from being run low on gear oil. So we swapped the whole assy, and as noted above just put the old haldex unit on the new/used diff to hopefully cure the massive amounts of network issues, and it did.

I tried to post pics but it fails for some reason.

[Hamfist]

Scanned today. Dem-0007, faulty pump. I guess I'll move it from the old carrier unit... Already moved the Dem, should have just moved it all when we swapped out the rear end, lesson learned. I know it all worked on the old one, just a bad bearing. Ugh

[hoonk]

Scanned today. Dem-0007, faulty pump. I guess I'll move it from the old carrier unit...

Hopefully the faulty pump did not fry your DEM

[Hamfist]

Hopefully the faulty pump did not fry your DEM

No other codes, we will see! Doing the swap after lunch

[Hamfist]

No other codes, we will see! Doing the swap after lunch

Well, put the pump in and that's still there. Now we have DEM-
0007 and DEM-000B

All the parts from the known working rear end are swapped.

The sweedespeed threads are suggesting the temp/pressure sensor In the Dem housing. �� And the pump, new filter and fluid.

I wish I could find a good tutorial on how to activate things and test the pump or read the sensor.

[hoonk]

I wish I could find a good tutorial on how to activate things and test the pump or read the sensor.

Have you seen these?

https://xemodex.com/us/knowledgebase...c90-2005-2010/

https://xemodex.com/us/knowledgebase/dem-flow-chart/