ABS kicks on when I am moving very slowly

Question

My anti-lock brakes engage when I am moving no more than 2-3 miles per hour. This only happens occasionally. Everything looks goods regarding my brakes (pads, etc.). They engage just fine in the snow and on wet surfaces, as expected. But frequently, as I pull up to a stop light or stop sign, the ABS will kick on for just about 1 second right before I come to a complete stop.

Any ideas on what might cause this? I took it to a couple shops, one wanted to replace a bunch of things for ~3k (not going to do that), and the other said they couldn't find anything wrong or even reproduce the issue. My brake pads/rotors are all in great shape, having been replaced less than 20k miles ago.

Driving a 2004 Chevy Tahoe Z71 that is going to break 300k miles this afternoon.

Answer 1

General Motors is well known for ABS problems.

The problem comes from the speed sensors in the wheel bearings.

The sensor slips into the wheel bearing and reads a toothed wheel inside. These sensors are very senesitive to the distance between the end of the sensor and the toothed wheel. When the gap gets too big the sensor can't properly read the toothed wheel at low speeds. The gap gets too big when rust builds up between the sensor and the surface of the bearing. This layer of rust actually pulls the sensor out of the bearing slightly.

It is possible to find out what wheel bearing is having a problem by monitoring the speed of all the sensors with a scan tool. The first sensor to drop out as you slow down is the problem child.

It is possible to remove the sensor, clean the surface and reinsert the sensor. It is difficult because if the bearing is rusty then the sensor is difficult to remove without breaking it.