I'm surprised no one commented that this is a very common problem for the 97 and some 98's. If the light just stays on, yes, by all means check the wheel sensors. However your problem is most likely in the module atop the ABS brake unit. It is poorly located close to the exhaust and is prone to heat failure. A couple of years ago, when mine failed, there was a huge amount of stuff posted about this. Some people managed to resolder the board in the module. The unit needs better heat insulation and a heat sink to get the heat away from the board before individual components are affected. You will probably find somewhere on the board references to a guy named Vitor. Vitor is actually Victor, here in L.A. If you send him your module he'll rebuild it for you at a fraction of dealer cost. Does a fine job, wonderful guy, and our 850 never suffered a relapse. Of course you need that silly Torx socket to get the unit off, but such is life. I suggest you try searching for "vitor" on the board, or "vitor ABS" perhaps.

Good luck!

DS