Abs light problems

What is your question?

I took my car to Toyota today to find out what problem is with the abs light. First I'm not having any problems with the car. They indicated the computer is not working and they told me it will cost 4000.00 to fix. They said it's not fault it's a bad part. My warrenty is over 3 years. So I what can I do I think this is a rip off