I have bought Volvo xc 90 2.5T 2005 with this problem.
I have check by local technician who works only with Volvo.
He checked and the problem is NO COMUNICATION WITH DEM.
He try to replace with other used DEM but nothing.
I leave for my reason and using only FWD.

One day I start to check connectors.
Start from YAW s3nsor,humidity no,corrosion no.
Check the connector of DEM,no humidity,no corrosion.
Measure the voltage 11.8 volt.
Measure the resistance of pump,5.6 ohm.
I open the DEM looking inside and no sing of humidity or burns.

Close everything and I go to service to change motor oil.
I have forgot to put the connector of pump in DEM.
I have done it,and AWD starts to works suddenly.
I have done 3 or 4 km and it was ok.
Turn of the car and turn on again,at dash again ANTI Skid SERVICE Required.

Can somebody with the same experience help me ?

L really like to have AWD.