The wheel speed sensors on GM trucks generate rather wimpy signals to start with, and anything that reduces that even more will make it look to the computer like that wheel stopped turning. In response the ABS kicks in to try to get that wheel turning again. On most truck brands the ABS stops activating below 3 - 7 mph, but even when they still do, most don't reduce stopping distances like on GM vehicles. The purpose of anti-lock brakes is actually only to maintain steering control, not shorten stopping distances, but most vehicles DO stop quicker when the ABS kicks in.
I assume you have four-wheel anti-lock brakes, not rear-wheel, and it's a 1500. GM has had a common problem where rust builds up between the hub and wheel speed sensor. That pushes the sensor away from the tone ring which weakens the already weak signal. Many people think they solve the problem by replacing the speed sensor, which will work, but the better fix is to remove the two front sensors and clean the rust off the mounting surfaces on the hubs, and to clean off any rust or metal filing on the end of the sensor.
If there was an electrical problem with a sensor, typically a broken wire, that would be detected by the computer which would set a diagnostic fault code, turn the system off, and turn the yellow warning light on to tell you. That hasn't happened so we can assume electrically the sensors are okay. They just aren't generating a solid signal. Anything that generates a voltage generates a smaller voltage as the speed decreases. That's why you get the false activation only at lower speeds. As the problem gets worse, the false activation will occur at higher and higher speeds.
Tuesday, August 19th, 2014 AT 9:28 PM