What triggers the rear ABS light?

[5.0Flareside]

Mine had started to come on about 1 minute into driving.. I have no idea why..

What are the things that can trigger the light?


Sent from my iPhone 4 using Ford Power

 

[blacksnapon]

Sensor, wiring, tone ring, ABS module.

 

[johny89]

RABS or ABS?
the rabs has a valve known to fail at the driver side on the chassis.