Sensor would be the first place I would start.
2 in front, 1 on each hub.
1 in the rear, on top of the differential, front side.
Rear is easiest to work on, and common after high miles. You can remove it and clean off the sensor to see if that helps.
Front sensors are expensive & since new hubs come with them, I would replace the hubs. You can check the wires on these to see if they are cracked/cut/broken, or if one of the connections are loose.
If the ABS light flashes, its something else. ABS off, the light stays on steady.