The ABS systems in the older cars (like ours, pre OBD II) run a diagnostic every time you start the vehicle. If it starts AFTER you start moving the car, then its a wheel speed sensor, vehicle speed sensor, or transmission speed input/output sensor. The great news is not all of them store abs code info so you may not get one OR a light. Just have to have your mechanic follow the directions he can get out of alldata (he SHOULD know what that is). They can be a grand beyotch.