Your ABS Control Unit may be reaching the end of its useful life.
The original design is weak and all of the 96 and newer units will eventually fail.
The ABS light will start appearing at random times and increasing in frequency.
You may have a dealer or a reputable independent Volvo service read the ABS codes; however, you may end up paying up to $125.00 just for the diagnosis.
Here is more information on another option to solve your problem, if you have a defective ABS Control Unit.
Vitor's web page
Click on the ABS / TRACS Repair link.

MY 97 started doing that, My abs mod went bad shortly after that
car had 60k on it

These vehicles develop intermittent electrical faults inside the ABS controller (which is attached to the ABS pump near the master cylinder). When mine, also a '96 850 started happening often I finally replaced the controller at a cost of around $500. Ouch.

This seems to be one of the parts on our vintage of 850 which will almost certainly fail on almost every vehicle at some point. Seems like a design weakness to me, but Volvo shows no signs of doing anything to help the effected customers. I think they like collected big $$$ for the part.

You can read more about this problem at:

http://www.volvospeed.com/Repair/abstrax.htm


John