This is a particularly acute problem on 96 850's and 98 70's. The module is beneath the ABS block, and in the 98, it develops cracks in the pcb wafer and/or the solder. The job is not too difficult for DIYers according to some of the recent posts. Part is $348 discounted over the internet, $416 at a Volvo dealership parts counter. The usual code pulled is rear ABS sensor...but it's the module.

PLEASE, PLEASE, PLEASE report this to the NHTSA for the purposes of data collection (perhaps they may eventually get Volvo to do something about this). You can do it in two minutes online at: http://www.nhtsa.dot.gov/cars/problems/ivoq/default.htm
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David \\ (98 S70 T5SE Black, misc mods (mostly lighting), red calipers) (92 940GLE)