I received a message in the DID that it was unavailable after a dealer installed software update a while back. I had to do something with turning the cruise control off and on to get it back.I have only had FAB engage ONCE, and it was what I would call a "false positive" event. As I was approaching my house I pressed my garage door opener and kept going at 5 to 9 MPH as I turned into my drive way. My driveway is at a slight incline and I guess when I turn in the car read to slowly opening garage door as an obstacle and SLAMMED on the brakes. It was SUDDEN and scared the crap out of me. It took a weird set of circumstances to trigger it.
In all of my other normal driving I have NEVER gotten into a situation where the car needed to respond. I'm not that gutsy.
So to the OP how do you know the FAB isn't working?