There has been a lot of traffic on this site about ABS, and I've begun to encourage EVERYONE to got the the NHTSA site and log the failure into their database -- http://www.nhtsa.dot.gov/cars/problems/ivoq/default.htm. The biggest problem years, according to 'someone claiming to be Frank,' a Volvo tech, are 96 (a wiring problem) and 98 (a module failure that some attribute to failed soldering on the pc board).

For 98, a module swap out is the prescribed treatment. (If it happened to me, my curisoity would warrant my attempting to fix it myself, but if there's a core charge, I'd lose it for sure.) Apparently the pc board is encased in a gel or other clear sealant. For a more affordable fix, find an independent that will get the part for less ($348 list) and install it without passing on the high overhead of a dealership service department. Be sure they can backup the 1year warranty.
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David (98 S70 T5SE Black, misc mods (mostly lighting), red calipers) (92 940GLE)