AWD DEM issues, 2004 XC70

[modfather]

Hey All,

I noticed a while back that the AWD on my xc70 does not work. This car has had periods of time with the battery disconnected in the past.

I finally got VIDA DICE up and running, it was showing an error for Oil Pressure, DEM Faulty. I cleared all the codes and took it for a couple of miles drive. Parked up and rescanned with the engine running and the code had not come back, plus i could see values for Solenoid and pump current, oil temp, pressure and dem voltage.

I know Dems do have a tendency to fail, do they go intermittently or did i get lucky?

I am going to be in that area doing some exhaust work and replacing the driveshaft. Trying to decide if i should do some sort of basic service on the haldex or if more might be needed?

thanks!

[Blacklab467]

So is the AWD working now then? Take it for a spin in a gravel alley or on wet grass to test it. If not, it may also be the angle gear input splines or collar sleeve.
I have not heard of DEM failures before although they are susceptible to water and road salt damage in certain climates.
Definitely change the Haldex fluid and filter and get the proper Volvo fluid, it gets really dirty and usually takes out the pump which is about $350USD. While you're at it change the rear differential fluid and angle gear fluid in the front, again with the correct Volvo spec fluid.
You can change the filter and fluid without removing the shaft and flange but you will leave much of the contaminant in the Haldex if you don't remove the pump. Pump removal will necessitate propshaft and flange removal which is a lot of work but will allow you to get all that dirty fluid out.
What was your reason for wanting to replace the driveshaft? Although not serviceable, these seldom give trouble and are very expensive. You can take it out and clean and regrease the CV joints at both ends and get some extra oil in the support bearing with a needle and syringe. The bearing rubber support can deteriorate with age and cause a vibration, I had to replace mine last year but got lucky and found a new one on a car at the auto wreckers. Volvo discontinued this part a few years ago.
How many miles on your car?

[vtl]

DEM failures are common. Some leak oil from Haldex, some corrode around cover's sealant or fail the rubber gasket around connectors and let water in. Usually the pump dies first, though. What exact DEM code did you see?

[misssophie58]

If the AWD system is not working, you should try driving in non-slippery conditions (like wet grass) to see if it works. You should change the oil and filter to help ensure more safety.