I just had the same problem. Your Abs cotroller is bad. My 1996 850 was throwing the same codes. The cost of a replacement unit is $387-$475 plus 2 hours of labor depending on dealer greed. Thousands of Volvo owners have had this problem. This is due to poor parts supplier quality control. May I suggest and alternative?

In your investigation of the problem, you may have noticed that parts dealers want your broken to unit (core) to rebuild and sell it back to people like you for big bucks after you buy a new unit. Why not find a core rebuilder through the internet and save money.

Do a google search on the internet using the key words "1996 Volvo 850 ABS Controller Repair". A website should pop up with a precise description of your problem and what to do about it. The cost of repair is 1/3 the cost or replacement.

Good Luck
PS you probably do not need wheel speed sensors because your abs unit is throwing bogus codes due to its internal breakdown.