That would be my suggestion as well.

1) If the light immediately comes on with the key and never goes off, check the fuse on the surge relay under the seat.

2) If the light comes on with the key, goes off once the car has started, then comes back on after you drive away, check and clean the sensors. They're magnetic, they can develop an obscuring layer of rust particles from the rotors. Not shiny clean, just remove the mass of magnetic dust on them.

If the ABS light still comes on, get out your handy dandy Bentley manual (make sure it includes the late model cars) and go to the ABS section. Unlike the Bentley manual for the VW Jetta GLX I sued to have (which merely said 'take it to a dealer already!) the Volvo manual has a very nice diagnostic that just take an hour or less and a multimeter and which should pin down the defective component pretty well.
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)