Brake Abs Warning Light problems of the 2007 Lincoln MKX

The brakes shutter when making stops and the pedal becomes hard then goes all the way down. This has happened many times whether at slow speeds in the city and highway speed, which almost led to an accident because the vehicle almost did not stop. Also the abs light comes on when driving on highway. I've had many parts replaced such as suspension front and rear, stabilizer arms in front, calipers, brake pads etc. But the vehicle continues to have this issue.