Check fault codes. Maybe there will be a P0500 which is for the speed sensor. It likely needs a Differential Speed Sensor but here is a diagnostic.
1. Check resistance of the Differential Speed Sensor (DSS). The sensor should indicate 800-2500 ohms.
2. Replace the sensor if it is out of range.
3. If the speed sensor is indicating proper resistance, disconnect the ABS module and check resistance between the Red/Pink (RD/PK) wire at pin 9 and the Light Green/Black (LG/BK) wire at pin 21. The resistance should indicate the same value as seen at the sensor.
4. If the resistance is different at the ABS module than what was seen at the sensor, service the open circuit between the ABS module and the sensor connection.