The light on my 2000 Expedition EB 5.4L just turned on. I have not done any brake jobs recently. When you turn on the car the ABS light tunrs on as normal. After about 3 seconds it turns off then comes back on and stays on.

What can be wrong? Is this something simple to fix?

The manual says when the light stays on that the ABS system is not working and is disabled. I've read in a thread that changing the ABS speed sensor on the rotor might correct this problem. How can I tell if the sensor is bad?

What else can cause this?