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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.

  • Welcome to the site. Which car is this? Make/model/year. – Zaid Jul 29 '16 at 19:14
  • @Zaid updated to add year/make/model – USER_8675309 Jul 29 '16 at 19:17
  • How are the wheel speed sensors? – Zaid Jul 29 '16 at 19:44
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    The ABS is going to kick in when it sees a differential in wheel speeds. One possibility is a sensor problem. The other might be a difference in tire pressure or some thing else that would cause a difference in wheel speed. The other would be a slippery surface. Can you reproduce the problem on demand? Could you try going back to a place where it occurred before? – dlu Jul 29 '16 at 20:02
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General Motors is well known for ABS problems.

The problem comes from the speed sensors in the wheel bearings. enter image description here

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.

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