On our '05 XC70 (185,000 miles), the "ABS Anti Skid Service Required" light is on (and has been for some time. I just almost got stuck in a snowy parking lot, as, with studded snows and AWD, I thought there should be no problem getting out of it. It appears that the AWD system is not working, though; front tires spun, but no work from the rear wheels.

Could the two be related? Is the AWD system at all related to a functioning ABS/Anti-skid system? I looked, and the prop shaft is still intact, but I do not recall whether or not I have ever checked to see whether the AWD system actually worked. We bought the car in 2018 with about 171,000 miles on it, and I guess the winter use has never really tested the AWD system. Any thoughts?

I had similar issue with 2004 V70 AWD when I could not drive up icy driveway. I put it on my lift and found that only front wheels spun when in drive. I did the diagnostics from the Xemodex.com website and found the pump to be functioning but the electronic control was faulty. I removed the electronic control (simple process) and sent it to Xemodex. They cloned the network address into a new one and returned it (fast turn-around-time). Installed the new control, changed the fluid & filter (difficult but not impossible) and all 4 wheels spin while on the lift. I did this last summer so had to wait for winter to really try it out and it has worked great. We've had lots of ice, slush, snow this year to test it. This is the second Xemodex product I've used and have been very satisfied.
Marlin

Thank you. Can the car be driven while the DEM is removed?

I don't think so. Seems to me that it leaves an opening in the haldex unit.

Thank you. I am remembering that I heard a loud "clunk" just before the front wheels started spinning (under hard acceleration). I thought I had hit a pothole, but thinking back, it seems that the noise was followed immediately by wheel spin. Any thoughts?

The DEM diagnostic flow chart at Xemodex.com is very nice and easy to follow.

Your loud 'clunk' could have come from anywhere. If you did hit a pothole, it could have messed with one of the speed sensors which disabled the traction control, allowing for wheel spin. You need to check the codes associated with ABS before spending money on parts or repair.
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Keeping it running is better than buying new

Thank you Klaus,

In your experience, do these systems (Haldex AWD systems) fail simply due to spirited acceleration? It seems that the car should be able to withstand that, but it is an aging car. Thank you again; I'll get it in to the mechanic before I start to panic.

Haldex fails due to lack of service, not the gas pedal. Your mechanic needs to check the codes for the ABS, DEM, and REM. Changing the oil and filter of the Haldex is not a simple task, but should be done periodically.
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Keeping it running is better than buying new

Thank you again, Klaus,

That is helpful to know. I doubt the unit has ever been serviced, but it's nice to know I didn't break it merely with exuberance.

Thank you,
Kevin