I am having problems with my abs system, connected a scan tool and found a code for left front wheel speed sensor signal missing. Checked connections and found them to be tight and clean. With the scan tool still connected i had a friend of mine drive and I pulled up the data stream and when braking occurs around 10 to 12 miles an hour the left front sensor shows the minimal value of 3 when the other two match and show their particular value at that time. When the truck is at a stand still all three show 3 as their value. On acceleration and coasting all sensors correspond but once you brake and the truck's speed hits about 10-12 mph left front wheel speed sensor drops of and shows 3 as its value again and actuates the abs system. The ball joints were just done and this started directly after. Before throwing a wheel speed sensor on the truck or digging deeper I am wondering if anyone has seen this problem before. I am also wondering why this is only happening during braking. Perhaps loose or broken wire or could the sensor not be close enough to the tone wheel. I have not ohm'd the sensor wires yet for continuity. Any advise would help. I have the fuse for the abs pulled until l can figure this out.