Car suddenly didn't break for one or two pumps, the brake felt hard, they didn't go down like there was something blocking it from going down and the abs lights went on for a second. We were going slow about 10 mph. We pulled over the breaks went back to normal worked fine. The abs lights have been going on and off for about 4 to 6 months prior to this incident. We are scared it will happen again we've been driving it but with caution. what can it be