There is no wear sensor on this bike, so either you ABS sensor is bad or just not seated correctly. Also check wiring for damage, unplug it at the connector and measure the Ohm's. Dont know what the reading should be but at least you know if it works at all, also measure the front, they should be close in reading's , if the rear is way off then you know it's bad.
Did you repair the FD yourself?
Got a replacement off another bike?
if you got a replacement off another bike it needs to match the one you had, different models have different number of teeth on the abs ring for the sensor.